In the only open adoptions with which I'm personally acquainted, the fact that there's no big secret and everybody knows everybody else and what all their peculiar relationships to each other are helps a great big whopping amount to make it easier for everybody to treat each other relatively normally.

"Relatively normally" in this case means "in just as neurotic a way as if everyone lived in two-parent heterosexual families and the two parents were the birth parents as well as the parenting parents, but with more entertaining origin stories. No, not as entertaining as Spiderman. Okay, maybe they're not all that entertaining."