Inherited tenant - parents living there refuse to sign a lease.

[Carly M.]

I just bought a duplex with an inherited tenant who is under market value in rent. She is paying $1,000 when the market value is $1500. I gave her a lease to sign that is month to month. The rent will stay at $1,000 for 3 months and then it will increase to $1,400. 

From what I know she has paid on time. The previous owners have had them in there and did trades for yard work in exchange for low rent. According to the tenant, a cupboard in the unit (before I owned it) fell on her and she is unable to work full time due to her injuries. What's more, her husband who was doing the yard work (and bringing in the money) for the previous landlord left her with nothing. She faints easily and her parents moved in because she can't be alone. 

When I went to have her sign the lease, she said she wanted to have her niece look at it. It's been about 4 days and I have heard nothing. I asked her if she had any questions, she said no. I said make sure to have everyone sign by Wed (1 week after giving her the lease). She has just informed me her parents will not sign because they are leaving in three months. I said to have them sign and we will make a new one in 3 months with only you since it's a month to month. She said sorry, they are not signing. 

So here's my question: Do I overlook it? Or do I make this the hill I die on? I'm worried if I overlook it, I will appear weak and she will do this with other things. I do feel bad for her and she's very nice but I am also not running a charity.

What makes it sticky is I live next door and see her all the time. And I think they are all illegal from Mexico. Her parents do not speak any English. Is there any liability on me with that?