We own and manage an 18-unit apartment building. We have an onsite resident manager who gets free rent on a 1BR in exchange for light repair and maintenance (no rent collecting). He has just moved his new girlfriend into his apartment. This is the third girlfriend in one year; his relationships tend to end badly, and he had trouble getting the last girlfriend out. He wanted to change the locks but we told him that would be illegal. He doesn't tell us when he has someone living there; we just figure it out. This time around, when we realized Girlfriend #3 had moved in, we asked him to submit an application and credit report for her and said we would treat her like a tenant and put her on his lease. He agreed. Our question is: is it legal for us to charge rent to this woman -- say, half the rent on his apartment? She is not helping him with his duties; only getting free rent. We want to do this by the book. Any suggestions? Thank you.