Women's rights in a divorce

My mother married into a family 4 years ago, when her spouse and my stepfathers spouses died. She is not working.My stepfather also has three children. He kept the money from the sale of my mothers' property at the time of marriage. Since four years, he has been inflicting mental torture on her daily, fighting with her about every small thing just to torture her, complaining about each act of mine, and repeatedly threatening to throw us out, or file a police case again us. He later claims it was all done in anger or pins all the blame on my mother. He has also cheated on her many times, and even admitted it to her, though we don't have any proof. My mother is finding it difficult to bear it, and has even started taking pills because of migraines due to stress, yet doesn't want to leave because Indian courts are infamous for granting small amount of alimony and maintenance.He has a large number of assets and leads a lavish life, however a lot of this is hidden income. I want to ask what options we have, whether there is a special compensation in such cases of abuse, how long the matter is likely to go on, the legal fees involved, and what we're likely to receive in case of a divorce.