Nothing you say or write to them will change who they are or how they behave. They aren’t self-reflective enough to take any criticism and apply it. They will simply dismiss it and say “good riddance”.
What you can do is leave. Just leave. If I were in your shoes, I’d get my important papers, whatever trinkets or mementos I wanted to keep and move them out over a few days. Nothing larger than what fits in a shoe box. I’d throw my clothing into some garbage bags and tell anyone who asked that I was cleaning out my closets and giving stuff to a charity or a friend or whatever. Then I’d leave for the day and never come back. Gone. Leave a note saying “I’m out.” so they don’t file a missing person report.