I agree with the sentiment about Abby's biological father and add that her mother would probably be proud of Abby. If the situation were as follows, then we could still discuss, but the way it happened, he doesn't deserve redemption:
- Initially trying to convince Jess to have an abortion
- Go to his family to clear things up with them and tell them what's going to happen
- His clique doesn't want to lose their buddy and starts the rumors about Jess on their own account
- Comes back and finds out that Jess is gone. No one really knows where she is now.
- Years later: They have a guys' night and one of his buddies blabs (alcohol loosens the tongue), he informs his wife and she encourages him to make contact.
Of course, this could not have happened. We know from what happened that he only gave his wife the most necessary information and even when the date for the meeting was set, he was probably still hoping that Abby wouldn't show up and that his skeletons in the closet would remain undisturbed. In my theoretical scenario, we can still discuss whether he deserves forgiveness, certainly more so than in the actual scenario, but in the actual events, not a bit.
I also don't see much/any blame on his wife here, as I said she was largely kept in ignorance of his actions herself while she thought she was doing something good for her children, Abby and possibly her husband. If she had known what he had done, she would probably have kept the whole story to herself or phoned Frank herself and left her husband out of it completely.
And on the subject of “Should Abby meet her half-siblings?”, I think the following approach would be the best, once she has worked through it: at least once in the presence of the children's mother and in Frank's presence. The biological father should never be present. After that, Abby can see how she feels and if it's ok for her, then she can optionally meet her siblings more often. If it doesn't work, the father can then explain to his children why the older half-sister is keeping her distance from them when they are older. But I think Abby could be a good influence on the kids: On the little brothers in that they never become like the shared father and on the little sister in that she never gets involved with a guy like the shared father.
Also: Abby should be really careful with what she wishes for. Her two wishes (“I've always wanted little siblings!” and “I've always wanted you (Lilly) and Dad to get along better”) have come true in a way she never saw coming. Alternatively, Frank should investigate whether Abby came into possession of a monkey's paw by chance.
