How do I prevent mom's brother from manipulating and taking advantage of her?

My mom (81) has an elderly brother (85) who comes to her house for dinner each night.  He now has started sleeping over at her house (he has a house of his own and money is not an issue) He now wants to live with her. It is loneliness. My mom told him he can no longer sleep at her house. Now she feels guilty and is reconsidering having him live with her. He is manipulative and takes advantage of Mom's kindness. What can I do?