Sister' marriage life

My name is Prasad, I’m from Andhra Pradesh and we are Hindus. I’m looking for a solution in my sister’s family life. My sister got married in 2005 to a government employee and they have 2 kids (girls) now. Her husband treated well for few years and then started harassing her for no reason. He also tortures my parents with vulgar words when they support my sister. I’m working in a Software company and they sent me United Status 2 years back for work related. From then he harassed my sister more than ever mentally and physically to get some money from me. So I have transferred some money (in lacks) to his account and to my sister account. We can clearly see his priorities are his parents and his sister’s more than his wife and kids. With the same reason he asked my sister treat his sister and parents very politely even though they didn’t treat her in same manner. Also my sister treats her mother-in-law and father-in-law (his parents) well even they didn’t. He built a home few years ago and registered it on his parent’s name. We gave 5,00,000/- dowry and 90 grams gold during her marriage, but he didn’t have a penny of property either on my sister’s or on his name. A month back, the issue gets bigger and he beat my sister, so she came to home with her kids as she can’t go anywhere and don’t want to go back. He also started blackmailing that he will give a lawyer notice if she won’t return back to his home. Please suggest us what to do. He purposefully put most of his properties on his parents name to deal or play in the situations. Thanks, Prasad