Family Business Share And What To Do

My aunt was married in 1987 in a business family. Her husband has 2 more brothers. Her father inlaw has combined business( showroom). Her husband has 18%share at that time. But in 1990 her father in law took share from his son(my aunt's husband) and made him sign for it and till today never got anything in return for the share her husband has given to his father. She has two grown-up unmarried daughters now and facing many financial and health difficulties now. Her house expenses are also given by her husband's cousin brother. Her husband is not doing anything for years. Her father in law is dead and given the shares to his other 2 sons. Can she claim anything now on behalf of her daughters or any other possible way to get something?