Shandy57 yes I was thinking the exact same thing myself, that the op’s mother was bullied into this arrangement and into continuing it.
What a nasty piece of work, I don’t care if they are mentally ill, you can have mental health issues and not use threatening language towards someone who has every right to end the free loan of space.
Interested to see what GSM suggests, I think you will have to instruct a solicitor, and also call the police to ask advice in the case he escalates, or destroys your property as he currently has access.
I think an email from a solicitor, restating the terms, that the police will be notified should his behaviour continue to be abusive, I’d also note the removal of his property should be done under supervision.
Can you change the locks then have the removal at a preplanned time under supervision?