<human>: I recently moved back home and was told by my mother that there have been subtle threats from our estranged father (who I have not seen in 7 years) in the recent past. I won't go into detail, but they are not threats the police could pursue, but I do not feel 100% safe considering he knows our address. 

My mother has decided she can't live in fear and can't afford to move, and neither can I for the time being. She believes they were idle threats, but I am still scared and a bit paranoid despite these threats being 6 months old with no follow up. 

The issue is with my younger sister who is the only person still in contact with him. In the past I had difficulty accepting this considering the horrific abuse my mother has suffered at his hands, but she has her reasons (financial mostly). I know she doesn't tell him everything, and not much about me, but I am unsure how much is said as their meetings are kept very quiet. I have voiced concern in the past, especially considering my sister lives in my mother's home and has most of her bills paid by our mother, but have come to just accept reality. My mother accepts it because she loves her daughter, and otherwise my sister is a great person but I see it as a slight betrayal.

My sister is now traveling overseas, her first trip since the threats, and I do not feel safe at home. I feel angry at my sister for telling him about her trip, indicating to him we will be at home alone without her. My mom plays it off, but I am still paranoid. I don't expect something to happen, but it is a scary situation knowing a few things I will leave out.

How should I handle the situation? How should I confront my sister who thinks nothing would happen and takes the situation lightly? She has a relationship with our mother's abuser and terrorizer WHILE she lives under her roof and he makes veiled threats towards us.

Give me the gist of the text in a nutshell
<bot>: Estranged, abusive father threatens our family. Sister still in touch with him regardless & takes it lightly. Feel betrayed and unsafe at home. How can I confront my sister?