Tenant appears to have someone living in the basement. Liability?

[Michael Cavicchi]

So when I purchased my first home (3 family) I inherited a tenant who happens to be section 8.  It's a husband and wife with 3 kids (on the lease).  Last night they informed me that he lost his job. Obviously that sucks for anyone but I guess in this instance at least the rent will now be paid in full going forward with no questions asked.

On top of this, lately I have noticed her 20 something year old daughter around quite a bit and have been having some suspicions about where she is living.  Well last night when I was there I took a look at the boiler and I'm kind of almost certain now that she is living in the basement.  Obviously this is in violation of their section 8 for starters but also it's a basement and I know damn well it's not a legal bedroom.  So other than the obvious of tell them to kick her out or tell them to start packing who is liable here if something happens? What if the fire marshal catches wind of it? Am I going to be fined? If something happens sued?

I mean it's not like I really am in love with them as tenants but I also know it's January and if I get them out now it's probably going to be quite a few months before I can get someone else in there but yeah not exactly pleased with being in this situation.