Need divorce from a drunkard irresponsible husband and their family

My sister got married 9 yrs back she is having 3 kids one girl and two boys(twins). Her husband is a drunkard. Neither he is working nor he is taking responsibility of his family. Since my sister got married and especially at my sisters second pregnancy his family including her sister mother nd father have harassed her like anything. At the time of pregnancy he told my wife to come to my parents place as it includes lot of expenses. He dont earn and dont pay a single penny for her kids education and their welfare. From last 3 yrs my wife is staying with my parents and my family is taking care of her and her kids. He drink every day and abuse my sister and our family. In this case we are planning for a divorce so just wanted to know that what is his rights for the kids??