I don't agree. Yes it is "her" wedding, but its a major family event. There will be all kinds of people there who she doesn't even know (distant great-aunts, friends of mom and dad), and who she will never again see after the wedding. But her brother will be her brother for the rest of her life, and their relationship when they're both in their 50's and have kids of their own will be much different than the one they have now.C Dick said:It is her wedding, so she should get final say. You could talk to her, and offer to keep your son on a short leash if she will agree to have him there. If she refuses, go anyway and have a good time. If she agrees to invite him, make it clear that he will be dealt with severely if he acts up. If it looks like it will be a disaster, make him an offer he can't refuse to be somewhere else, 19-year-olds like vacations.
I invited some but not all of the relatives I despised to my wedding, the one I despise the most acted up. In retrospect, I should have not invited any of them, and screw the people who would not have come because of it.
But if they aren't yet mature enough to realize that, then it's Dad's job to prevent this day from becoming a black mark in the history of HIS family. There are more people involved in a wedding than just the bride and groom. That might be a difficult concept for some people to buy into, in our world of self-empowerment and me, me, me, but in our Grandma's time, this would be a no-brainer. The whole family would attend the wedding, the whole family would behave, and dad would actually have the balls to tell them to stop their snivelling and whining and GET ALONG.