K.Y.
Hi,
Your basement apt. is probably not legal, and since it is not, your mother will probably be faced with fines and asked to correct the situation by removing the bathroom and kitchen from the basement. That's the bad part, but since it is not legally a livable space, he can not stay there either. I would call the Dept. of Buildings to have an inspection done, again, you will have to pay fines, but at least you can get the inspector to condemn the place and he will have to leave. I would also start an eviction in landlord/tenant court immediately. I'm no legal expert, so all of my advice is just based on what I *think* I know, so you should contact a lawyer today and start the process since it could take up to 6 months to get a tenant out. GL!