You can't choose your family but you can choose how you react to them.
If they wind you up so much, find a convenient excuse for the day in question and don't go. There's no law that says you have to, and while you can hold your head up in the knowledge that you did the best you could for the people who needed you, they are grown-ups now and must look after themselves. Make an especial effort on the day to surround yourself with positive activities and people you like, and forget the rest.
The past only exists as a memory and what matters is now, and the future.