My view of the situation concerning Abby's biological father and his later wife:
The guy got a girl pregnant and because she wouldn't have an abortion his friends and he started a bunch of rumors about her that any of them could be the father, effectively bullying her out. His later wife somehow found out that he had impregnated a girl when he was about 20, and she was bullied into making him face up to his past.
The fact that she, as a mother, then had to hear what her husband had done with a young woman and got angry with him is more than justified. If I remember correctly, they both have daughters themselves. How would he react if this happened to his daughters themselves? Would he be justifiably angry with the guy or would he say “ That's too bad girl, you should have kept your legs together”? Because let's be honest, if he was mad at the guy in that situation, he'd just be a complete hypocrite.
I get the impression from him that he only admits what he can't deny in the situation. His wife didn't know about it for a long time, finds out by chance and forces him to face up to his actions. She then finds out exactly what he did and what happened after he can no longer deny it. Personally, I wonder if he has more skeletons in his closet that his wife doesn't know about.
Yes, both of them are responsible for the contraception, but I think that the least he could have done would have been to at least support her financially if he had no interest in the child. You could bring up the gold-digger argument, but personally Jess doesn't come across to me as that kind of person, more as a person who places a high value on family and friends and has had a rather unfortunate hand with men.
Should Abby meet her half-siblings? I think at least one meeting without the father, just with the mother and Frank when she has worked through the situation again is perfectly fine. Then she can decide how she feels about her half-siblings and see if there will be further meetings or not.
My post may seem chaotic, so I'll summarize it briefly: The guy is gross, his wife's annoyance is justified, and at least in the brief scenario she didn't strike me as unlikeable because she offers to meet Abby's siblings but doesn't try to persuade her to do so but leaves the decision up to her. And finally: in a situation like this, I would rather be like Frank than Aaron or Trevor.