If they intend to create a DuckTales episode featuring Della's unknown husband/lover and the boys' unknown father, I'd wish that it would take place somewhere before, during, and after Father's Day:
One day, the boys are having fun at the park and when they see how most children are having fun with their dads mostly and one of them asks them: "Isn't having a father the greatest thing in the world or what?!", the boys suddenly go into a slightly deep depression when they learn that tomorrow is Father's Day.
Later, back at McDuck Manor, they are seen sitting by the pool next to the boathouse with their feet in the water as they sulk. Scrooge enters the scene as he tries talking the boys into going on another adventure but when he notices them sulking and acting sort of unresponsive, Scrooge is concerned and tries to find out what's wrong until Donald intervenes and reveals to him that tomorrow is Father's Day and every year, before, during, and after this event, the boys undergo some kind of depression considering they never knew or had a father in their lives; other than the fact that Donald never told them much about him either, so, Donald decides it's best if he and Scrooge let them get over it until the day is over. Having clearly understood the situation, Scrooge and Donald leave the boys to do their thing.
However, as soon as their uncles have left, the boys decide to ask their mom about their dad even though the subject might hurt her probably. Having been the one more than determined to find their mother in the first place, Huey and Louie send in Dewey to ask their mom while she's busy doing the dishes inside the boathouse. Dewey greets his mom who returns the favor in response. Dewey asks: "Mom, can I ask you something?" to which Della replies: "Sure, you can, honey. You know that you can always ask me anything." However, once Dewey asks her the very question, Della suddenly stops and drops one of the dishes on the floor in shock. Realizing that what he asked her must've really shocked her, Dewey decides to forget the whole thing and leave but Della kindly insists that he stays while reassuring him that she's not mad or anything. Knowing that her kids are old enough to know the truth and that such a subject can't be kept a secret forever, Della decides to stop doing the dishes and have a heart-to-heart conversation with Dewey while calling out the rest of the boys to come in and join in the discussion, whom she somehow knows are trying to listen in on the conversation as well. Della and the kids gather in the living room where Della begins to tell them a few things about their father: what he was like, how they met, and so on... but fearing that everything about her husband/lover might prove to be a bad influence on her kids and lead to bad things for them, she finally concludes that there are just some things that they are better off not knowing about their father in the end; implying that their father may not have been a good man and that he had made some bad choices and done some bad things in life. With that in mind, the boys leave and Della resumes her work on the dishes, not knowing that they are being watched by a mysterious hooded figure spying on them from the outside.
In the evening, to make it up to everyone, Della decides to take everyone out to the city and have fun. However, on the way, with their backs turned and Louie busy on his phone while walking without paying attention to where he's going, Louie suddenly finds himself about to be hit by a truck heading his way until he is rescued by the hooded man. Before Louie gets a chance to thank him, Della, who is under the impression that he is attacking one of her kids, subdues him until he says: "I see you haven't lost your touch, baby despite circumstances." Scrooge and the others later join them. Recognizing the voice and speech pattern, the hooded man finally reveals a face only the adults seem to recognize from the past. "Hello, Dellster." says the man. Intrigued, the kids ask how they know each other, which unfortunately forces Scrooge and the other adults to reluctantly reveal that the latter is, in fact, the boys' long-lost father, Mr. Duck. Though shocked, the boys are overjoyed to finally meet their father but their joy and attempt to embrace him for the first time is cut short when Della restrains and forbids them from approaching him any further. Then, Della lets out her anger on Mr. Duck, stating that she wants nothing to do with him, whether in life or death, as she had spent years trying to forget him and keep her family away from him and his mistakes as payback for leaving her despite the note he left behind explaining why he left in the first place, which somehow left her heartbroken.
Nevertheless, Mr. Duck explains that he had to leave in order to protect his family; given the fact that he was a wanted criminal in a mob led by his own uncle who raised him ever since his parents died in a car crash when he was very young. Unlike most members of the mob, however, Mr. Duck was one with a good heart and despite having a bit of a liar and a thief, he never killed anyone or lied to Della about the fact that he loved her and her family despite certain differences, otherwise, he never would've left in order to ensure their safety; especially, their own children, whom he feared would follow in his footsteps eventually, while evading the law AND his uncle who has placed a price on his head for his betrayal at the same time. When Donald further points out that he wasn't there for him and the boys after Della's disappearance and how he spent years raising them on his own with money he received from a company that contributed to the poor, Mr. Duck replies: "And who do you think sent you that money through them in the first place, Donnie? (Donald is puzzled and he continues) That's right. After Della's disappearance, which led to a near-family tragedy, and you left your uncle with the kids when they were still just eggs, I knew you wouldn't have a chance in raising the boys on your own with the little money you had left to keep your house afloat. So, I had to do what any father would do to make sure his family stayed alive and well. I sent that money to the company, told them you were poor, and made sure it was delivered to you every time. And you may rest assured, that money was earned legally without any need for begging or stealing it. I tried going straight and started working part-time jobs while earning the money you all needed more than I did to survive. And whenever I didn't find myself being chased by the cops or the mob, I made it a habit to drop by the boathouse and keep an eye on you as I watched the boys grow and at the same time, learn some tricks and develop almost the same personalities as their own mother as time went by. It wasn't until you had that job interview 10 years later when I learned that you and the boys had been living with your Uncle Scrooge while going out on some daring adventures afterwards. But that didn't keep me from doing what I've been doing for the past 10 years and on either way. Then, when news of your miraculous return spread throughout the world, Della, I knew that you were all one, big, happy family again. And I, for one, never gave up hope that someday I would find my way back into this family when all my troubles were finally over." After what seems like a warm, heartfelt speech that has touched everyone including a somewhat doubtful Scrooge, Donald, and Della, Mr. Duck finally earns his sons' love, approval, and respect but he decides it's best he leaves before trouble starts heading their way after realizing he has spent too much time with his family whom he might've put in danger, stating that Della was right to assume that "there are some things better left unsaid about him."
At night, back home, Della returns to her room, wrestling with her thoughts about today's unexpected turn of events then, she takes out what seems to be a heart-shaped music box locket from her jacket, originally given to her by her former husband/lover and opens it to hear the music played. After she closes it, however, she hears the tune still playing until she notices Mr. Duck behind her, carrying another music box locket like her own. "After all these years and you still had it with you." says Mr. Duck before Della, though distraught, kindly asks him to leave, which he does with good comprehension. Unfortunately, unknown to anyone, Mr. Duck finds himself kidnapped by his uncle and the mob as soon as he leaves the manor's gates. Later, at night, the boys decide they want to go out, find their dad, and get something for him for Father's Day despite the dangers.
The next morning, Scrooge and the others wake up to find the boys missing with a note they left behind and decide to go after them before they get into some serious trouble. After buying their Father's Day gifts, it takes the boys a while to track down their dad until they find and deduce that he had been kidnapped and taken to an abandoned warehouse where they find him being tortured by his uncle and his men for information and in retaliation for having left the mob which is considered betrayal to him. Luckily, Scrooge and the others find the boys just in time and get them to come back home and not interfere with what's going on with their dad until the police arrive. But things go from bad to worse when Scrooge and the family find themselves captured as well. Then, they are taken to the boss and the rest of the men. "Leave them alone! It's me that you want! Not them!" shouts Mr. Duck. Despite being angry at his betrayal, the mob boss offers to gives his nephew one last chance to redeem himself and rejoin his gang; provided no harm comes to his family either while threatening to kill both him and his family if he rejects the offer. But knowing his uncle who is not likely to leave any witnesses behind; whether family or not, works up the courage to reject his offer. So, his uncle proceeds to shoot him until he decides to make him suffer by allowing him to witness him killing his family first, starting with one of the kids. However, such an act of monstrosity drives Mr. Duck into a fit of rage as his anger finally gets the best of his uncle and some of his men while shouting: "Nooooooo!!!!", which saves his family and allows them to escape unharmed while being pursued by other mobsters.
During the chase, Mr. Duck and Della bump into each other. Despite not the best moment, they find the time to reconcile as they confess their love and true feelings for another until it is interrupted by gunshots fired by Mr. Duck's uncle. The two separate as the mob boss mockingly compliments them on how cute a couple they make until he suddenly reveals that he was responsible for Mr. Duck's parents' murder. As it turns out, the mob boss knew that his own brother was going to leave him after he met, fell in love, married, and had Mr. Duck with his wife in order to begin a normal life with a family. Having considered this as an act of betrayal, which reflects Mr. Duck's own, the mob boss killed his own brother and sister-in-law and arranged for their murder to look like an accident in a car crash, thus, rendering his own young nephew an orphan whom he chose to raise and groom into working for the mob rather than to kill; a decision which he now regrets having made and chooses to correct with bullets the same way he did with his parents. Angered by this revelation, Mr. Duck manages to subdue his uncle and escape in order to rejoin his family.
However, after the rest of the mobsters have been dealt with and the family is reunited, unknown to them, the mob boss, having partially regained consciousness, aims to shoot Dewey or Della first until Mr. Duck rushes in, pushes him/her out of the way while shouting out: "Dewey/Della, look out!", and takes the bullet for him/her instead. Then, Scrooge uses his cane to disarm and knock out the mob boss. Though horrified, Della/Dewey is touched by Mr. Duck's sacrificial attempt to keep him/her safe until police sirens are heard approaching from a distance. Everyone proceeds to leave while taking Mr. Duck with them but the latter refuses, knowing that his injury will only slow them down, his absence from the scene of the crime, and his presence at McDuck Manor or the hospital with the family will only make it worse for them. So, he demands that they leave him in order to make it out safely while stating that he is finally ready to accept the consequences of his actions; whether he makes it out alive or not. The boys refuse to leave their father behind but he tells them that they must go now and if anything, that they are better off living with their mother than they are with him, knowing they'll be safe with her from harm's way. Then, they leave, but not before a tearful Della, the kids, and the others somehow embrace him as a family member, Scrooge and Donald finally learn to accept him as such, and the boys finally give him his gifts for Father's Day.
Later, Scrooge and the family come back home only to find Della's music box locket hanging on a doorway, opened, playing, and with a note inside. It is revealed to be from Mr. Duck, having survived his injury from the gunshot, which merely grazed him, and having escaped before the arrival of the police at the warehouse. In the letter, Mr. Duck apologizes for everything as he expresses his fondness of each family member in his own way. He also reveals his intentions to someday return to the family for good once this mess is cleared and forgotten and the rest of his troubles are over despite not having to worry about his murderous uncle and his men coming after him ever again. A promise he intends to keep to the very end as well.
In conclusion, he states that he couldn't have been more proud of his sons than he has always been even after all these years of watching out for them in his own sneaky way up to a point where he also states that he couldn't be more proud to call them his sons at last while complimenting them on their gifts as well. Then, the same music from the locket is heard from a distance where Mr. Duck is seen carrying and playing the music from his locket to Della one last time before he closes it, waves good-bye to his family, and leaves.