Your mom paying with money orders with her name on them doesn't mean she's created anything better than a weekly tenancy at will.
You are free in the absence of further action to petition the local court with a complaint about the landlord's partner threatening you and asking the court to issue an order telling the landlord to knock off the nonsense and issue you a notice to terminate tenancy and then an eviction action if you refuse to move out -- as the process requires. That would be true in most states even if she hadn't been accepting rent with your mom's name on the money orders without questioning the named tenant about why someone else's name was on money orders. That's not dispositive of much other than possibly your friend getting someone else to pay his rent for him, in the absence of her knowing you moved in ... in violation of the lease terms, I'm sure.