NTJ. Victor will never figure out HE'S the problem until people tell him he's the problem. And let him deal with the consequences of his own behavior. He just didn't want to hear the truth. However, your partner telling him what you said gives me pause. And the fact that he is not seeing his part in his friend's problem. You can't change either of them. They need to see it for themselves. Try not to tell your partner his friend is an a*s. Just stick with how YOU feel. "I feel upset when he doesn't treat you with respect." So you don't become the jerk.
I know I'm late to this one but holy cow man! Her symptoms are how my allergy started. Doctors and everyone were sure it was just lactose intolerance...until the pill didn't keep my throat from closing up. Figure it out. Even if she left your selfish...self.
It sounds like your sister is the golden child. And she was tarnished when you got in a great university. Could it be her attitude? Maybe consider getting the apology but by no means do you have to. It isn't up to you to help her and your parents feel better. It is up to them to prove they really are sorry. But it sounds like they just want to apologize just to make themselves feel better. NTJ. You get to decide what you allow in your life. Maybe mom and dad need to admit their part in this before you even listen to your sister. Suggest a mediator or therapist so you 3 can talk. If they can get over their stuff, maybe then.
NTJ. This whole "blood only" garbage is just that. I would be more concerned about why DH was NC with MIL for a decade. While the world is not fair, kids will learn that outside the family. They don't need family to treat them like garbage as well. You and your husband are in agreement about this. You might let her visit them at your place but alone time is off the table.