Relative in the nursing home and a tenant is trying to take over his life and his finances by power of attorney. What can we do?

OK, if he is already not competent then he cannot validly give or change the POA. Guardianship would offer better protection if you can get it. Time to lawyer up, unfortunately. You did not indicate he has already agreed to change the POA or signed something...if he didn't, do you have the option to just get him the heck out of there?

He could revoke the POA and assign it to one of the caring relatives. You could help him notify the banks of the change.

You might also want to start eviction proceedings if she is not a responsible tennant.

If you can prove his thinking is not good and she has lots of problems take it to an attorney. Find someone who can help you in what you do.

Well, round up the posse of caring relatives, who can convene a fair and impartial trial of the accused, tar and feather her and run her out of town on a rail. Hanging is too good for her.

Why did he give a drug addict POA and not a family member?

If a relative is in the nursing home and a tenant is trying to take over his life and his finances by Power of attorney. He is very confused
and afraid of this woman. She is a known drug addict. She is trying to wipe his account out. He has plenty of relatives that care about him dearly