Did you see the article from Penny about the tree?

I can send that one to you if you want, show it to your MIL

Is your MIL willing to REFUSE him access to the rental if he asks her for use of it to move out?

I think he's better off living where HE is and YOU moving out... If he moves into the rental then you wont be ablet o get in there nearly as easily and he will feel like he has a safe place to hide.. if you move into the rental then he has to stay at home and live iwth his mother glaring at him in disapproval