Sister's husband threatening to kill and not paying any money

My sister got married in 2000 , after 2 yrs of marriage, her husnabd, sister-in-law, monther-in-laws and father-in-laws started torture her physically and mentally and asked for dowry. Till date she has never put any case again them as my sister is always thinking for prestige issue for families and what society will say. Now my sister has 18 yrs son and they are staying with father-in-laws house. Husband, mother-in-laws staying separately in company's house in the same city. Her husband s end a court notice to leave his father's house and my staying with him. But my sister is not feeling safety to stay with him in the company's house as he always threats him to kill her. Her son is also not willing to stay with his father in company’s house. Her husband has never given any expense cost to her as my sister is staying with father-in'laws (food,cloth,medicine cost etc). she wants ,she will stay separately,but husband will bear all the cost.