Contest divorce

My sister doesn’t want to live with her husband as he doesn’t care about her and kids. He’s always drinking and sitting idle at home. My sister wants to separate and get a divorce. But, he refuses and threatened to kill Her and The kids. He’s away from home somewhere and we don’t want him to come back. He wants to come back to her now because he doesn’t have any money and wants to use her for money. We are afraid to complain to police as he may get mad and kill himself Or others holding us Responsible. Don’t know what to do. Please suggest!!