What should I do?
She is not JW and they are allowed to sleep together. I don't understand why my mom, grandmother and aunt are allowing this to happen.
What should I do?
Personally I don't feel comfortable with telling people what to do. I don't know her or you, and the information you provide is rather minimal.
That said, I do feel comfortable with suggesting to follow universal precautions, and basic family rules (pay rent, get a job, no criminal activity, no disrespecting anything or anyone).
Good luck.