@Motts - the fact your sister made someone want to break up with you is truly nasty, and very unfair of her, though I suspect she knew and as you said before, didn’t want to take responsibility. She blameshifted to you as she didn’t see what she was doing as wrong, as people with narcissistic tendencies think everything they do is right, sometimes even including illegal things.
I’m currently grey rock with these relatives - well, cordial and polite rather than true grey rock boring. Most of them I literally only see because I still live with my mum (long ish story), but if/when I get my own place, I likely won’t see them much, if at all.