mycartist,

I would first look on why you want to stay in contact with your uncle.  He is toxic.

Reach out to your cousins and aunt and let them know for your own health, you will no longer have any contact with your uncle.  Emphasize that you do want to continue to have a relationship with each of them but it won’t be with your uncle around.  Ask them that you hope they understand and that you cannot be with them if your uncle is there too.  You need not give any more explanation or excuses.

Block your uncle from your phone, social media, etc.

Let go of your peacekeeper role.

Mark