Harassing Mother-in-law

It has been 20 years since my marriage, my mother in law does all possible actions which may provoke a verbal argument between my husband and me. My mother in law has two sons and two daughters, she would never acknowledge that daughters also have to serve their parents all she expects from us is that we keep pampering her daughters and giving them gifts. Her ill mentality has been a cause of her younger daughter's divorce and now she wants to see my marriage broken. She has been trying to socially isolate me, since all these twenty years she has rarely stayed at her elder son's place which is a four BHK flat in Mumbai ( my husband is the younger of her two sons ), I never told her that she move to the elder brother's place but she keeps on calling up people and relatives and passes abusive gossip about me which includes that I don't want to let her be at my place (Although out of the 20 yrs of my marriage she has been here for nearly 16 yrs), I don't cook and give her food, I abuse her and I am greedy and want to take away all my husband's property. My mother in law has two bungalows in her name, but she doesn't let me have my right over my husband's house which he bought independently. She keeps on provoking house help and maids against me and has successfully washed away all my reputation in my neighborhood. She also targets my mother saying that I want to bring her to my place and that's why I'm not letting her live here. Her two daughters having been very active in propagating vicious and fake content about me and she speaks to both of her mostly for an hour everyday, locking her room. I don't want any kind of punishment for my mother in law as she is quite old and even after proving her wrong the society will consider me as an evil and this will simply ruin my marriage. I have a young son and want to see my family stitched together, the only thing I want is that what legal step shall I take which simply issues a warning to my mother in law and her daughters so that they stop their really torturous propaganda against me socially. If just I can notify them that what they are doing is a crime and grossly illegal and they stop then I will happily forgets all their bad deeds of the past and start afresh. I don't have any objections in serving my mother in law I simply want here to stop her indirect or direct propaganda against me and filling my husband's ears against me.