My brother in law, moved into his Grandmother's house. She lives with her daughter. He signed a contract saying he would be on time with payments and once he sold his house would be able to buy this one. He hasn't paid anything and moved out because CPS was called on him. He is verbally abusive to his mother and his family and will not take responsibility for anything. He did some work inside the house (no one asked or hired him to) and is now making "renovations" to it. I use that term loosely because his work is subpar. He now has a "for sale by owner" sign in the yard and is attempting to sell a house he doesn't own. He also expects to be paid for the work he did on his own. Grandma owns the house the money is hers.
I think I would find out what this man is actually doing and see an attorney to shut it down. It sounds like grandmother is not strong enough to handle this issue. She needs help on it, IMO. It would be a good time to see who does have Durable POA and get that taken care of.