Please take care of yourself.

The longer you allow him in your household, the harder it will be to have him leave...them... leave.... legally even.

I hope you will be able to refrain from any physical fighting. The older adult is nearly always found at fault when it comes to the law in these matters. I know of someone who was egged on in his own home, and punched the unwelcomed step son (who didn't live there, and was an adult, who caused the problem..) and the step son sued and won against the home owner/adult.

Make some rules...if you can have a sit down session with the whole family to do this, that might work. Write the rules and the consequences. That way everyone knows (and hopefully agrees or moves out.) TC.