Babu Sir,
you have bluntly written that your sister was thrown out of her matrimonial home. Fine. You are planning to go to the police, the lawyers etc. did you find out from your sister what exactly happened? Find out. And cross check with the other side. Hope your brother in law was sane when he married your sister. Well no sane person will throw his wife out without ample reason. I presume you are her unmarried younger brother. If married, you will surely have an inkling as to how these madams go about their lives. And you won’t be writing. Go to the police or court and she is going to be a noose around your neck. If after eight years , if she can’t get along with husband she will not get along with your future wife also. I don no about your sister, but you sure, are couting trouble.