Should I host a party for My brother in law who talks bad behind my back?

Recently I found out brother in law and mother and law talks badly about me behind my back. They was confronted and denied everything even with proof but my husband and I decided to let it go because no one seemed to be being honest so the best thing we can do is drop it but be distant and limit seeing the family because now I don’t trust them. My husband of course has forgiven them but I have not so I choose to not go to most events with his family knowing the things they said and think of me. His family is very judgmental. But Anyways, the brother in law is having a Engagement party and the mother in law asked if I can help by creating the games for the party but I decided I do not want to help or even go. I’m happy he’s getting married and finding love but I don’t have it in me to go out of my way doing anything special for this guy knowing he speaks badly of be. I want to be the bigger person and drop everything, but I’ve been so kind for so many years and they still talk bad about me. I’m so over it and idc about impressing them or pleasing them anymore. I am still nice and respectful towards them but I lost all trust with the words said to me and about me. I dont know what to do do.