My sister's husband committed a very serious offense causing a rift in the entire family. My sister believe?

My sister believe in her husband innocense and sever our relationship. My mother's sister has continued her relationship with this man and my sister and participates in all events with them. She says that we are all her family and loves us the same. We have minimized our dealings with her and ist when she is in need, however, my husband, children and I resent her attitude; we believe you can't serve two masters. My daughter (who was the victim) is getting married and I don't want to invite this aunt to the wedding. I want my daughter's wedding to be a loving and peaceful event. Would it be wrong not inviting her? We are not inviting my sister and her family either, and this is very sad because her children (my nephews) wouldn't come. This is such a mess and I'm very stress about it. Please help!!