Sister's addicted husband

Hi, my family is going through a difficult time, we are so upset about my sister's husband. From almost last 3 years he has started spending a lot of time outside the home, he used to tell my sister that he is on official tours but off lately we came to know that he is involved in a lot of things - alcohol, betting, gambling, and now girls as well. Six months back he was arrested in a case where in he and another boy were caught in a car with 2 girls. That's so shameful for me to describe as well. Anyways my sister spent money and did her best to release him on bail, after that he apologized to my sister but did not accept any relationship with any girl. My sister got convinced one more time, but about a month back again he was caught in another controversy where a girl claimed that he spent his days and night with that girl since last 2 years and she was the same girl who he was caught with when he was arrested. Now my sister has made up her mind, she doesn't want to stay with him. Long story short, he is a moron and doesn't deserve my sister. My sister has two small daughters aged 6 and 2. Can someone please guide what should be th right thing for us to do? Should we hire a lawyer and send him a legal notice? I guess to get divorce court gives some time, my sister is working but her single income won't be enough to lead a good life. So my question is that is there a way we can file for divorce and he pays the maintenance to her on monthly basis starting soon or do we have to wait for the whole process. Please advice. I'm currently in Canada and my sister is in Delhi with my mom and her husband's place is in faridabd. She also works in faridabad as a teacher and she can't commute to her work place from my moms place as it is too far. What should we do? Thanks for your advice.