I called the cops on my sister's drug addicted bf today... need your help

Hey.. I have a sister who's been under the influence of drugs for years. She's a loser and doesnt work. She has a bf also on drugs and is equally a loser. Years ago he threatened my life and my mother's and creates a nuisance. As a result, I warned him not to enter my house ever. As such, I told my sister he's not to enter my house.

Today my sister sneaks him into my house into her bedroom behnd my back and when i find out all hell break loose. I find him half naked on my sister's bed, on drugs and threatening my life and walking around like a half dead zombie.

I call the cops and they said they cant arrest him cuz "my sister invited him" into the house, even though she pays no fuckin rent and its not her house. The cops said that in order to help the situation that they suggest I ask my sister to leave. If she doesnt that I should call housing court to throw her out. They said I cant kick her out cuz of squatters rights.

My sister is at the root of the problem of my life. While she's living here I dont know what else to do. She takes drugs and doesnt care about herself and doesnt respect me nor my boundaries. I'm very nervous now.

I ask for your help. Let me know what else I should do cuz I'm very angry and enraged and its upsetting my mom's health. She's 93 years old btw and it affects her nerves also.