Should we cut off family for not inviting us or all of our kids to parties?

My sister-in-law doesn’t like her brother or me. There have been several times where she throws parties and excludes us. I really don’t care to go as I don’t care for her either, but my boys want to play with their cousins, so I bear it when necessary. Just recently, my oldest went to one of these parties, and I wasn’t thinking anything till after when I realized that my other two are left out continuously because of this immature nonsense. It made me a little angry, and now I’m thinking of just saying no to my oldest going if all three cannot go. This time when he came home, he asked me why everyone else went, and his family didn’t. I made an excuse, but I don’t think I should have to do that. Am I wrong to keep him away? This is annoying