my tenants is always asking to be let into the apartment

[Candace Aul]

I own a duplex and I live on the first floor and rent out the second floor. My tenants has two people staying with her, and they are constantly knocking and asking to be let inside the upstairs. Tonight it escalated and one locked out the other and so they came to me and put me in the middle of it all. I want to be done letting them in. Anyone have any advice for me, please?