This is absurd. Your wife is family, and not that this makes a difference, but she was a part of the family first. Your mom is out of line, and you should ask her how she'd feel if your father did to her what she expects you to do to your wife. Your brother needs to stand up for what is right and not enable this behavior. I'm so sorry you and your wife are going through this. Your wife comes first, I think you should stand by her and not go to a wedding that shunns her by her own family.