Daugher in laws property rights

Want to ask what if father in laws do not give anything to his son and daughter in law. The case is my sister married to a well business family but just after year the start troubling my sister may be because we didnt provide the dowry. When they tourchered her so much my sister and her husband start living on a rental home apart from the in laws home. But there is no earning source for them now as they take back a shop which use to be run by my sister's husband. The non movable property is not earned my father in law of my sister but its inheritance property. My sister has two kids. What is the right of my sister and sister's husband in that property which is inherits not acquired by father in law. Is women commission will be helpfull because morally it seems not right to leaving them without any source of income. I also want to clear that the shop was runs by my sister's husband from 15 years. The in laws are not good people they also hide the fact mother in law actually is a step mother of my sister's husband. Please guide and suggests how to get a legal part of property by which at least they get a source of income to run their daily life. Regards