Hard to say, since literally all we know is that they're going to be present. A lot of the speculation is that they're going to turn out to be Webby's long-lost siblings, with Webby being merged with the comics character of April. As for what role they're going to play, it kind of depends on their situation. We don't know whether Daisy's going to show up with them in tow, or whether someone is going to randomly run into them, or anything. We're not likely to find out for another month, either.

If they are indeed Daisy's nieces then I'm surprised there will be only two of them instead of all three. For now it's hard to tell since all we know about them are their names.