If he has no lease you may ask him to leave, then if he doesn't call the police and say he is trespassing, the police won't help then you may evict him by using the court. take care.
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YOU need to see a lawyer. There probably needs to be a probate before anything can be done.
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If your mother's mother did not have a Will, there is a chance that your mother and her siblings all own interests in the house. In that case, your mother and her little brother would have equal rights to live in and use the house, and it may not be possible to evict him. Your mother, on the other hand, would also not need to pay rent to live there, if she owns an interest in the house. And, if he's violent and destructive, she may be able to have him arrested and taken out of the home when he causes trouble.
I agree with Mr. Ashman: your mother needs to see a lawyer as soon as possible. The lawyer will need to help her figure out exactly how her late mother's house is currently owned and what, if anything, can and should be done to address the situation with her little brother and her other siblings. It sounds like a mess.
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