Dear we asked her for a year to get out:
As long as you stay in the "asking" mode, you will not begin the legal process. The basement tenants may have rights. Your sister is a tenant.
I do not believe any attorney answering your post would suggest you attempt a difficult lawsuit on your own. So you should bring this family problem to an attorney.
Meanwhile, you should become sensitive to your rights as a landlord in the New York City Housing Court:
The answer provided to you is in the nature of general information. The general proposition being that you should try to avoid a bad outcome if you can.