Depriving of property

My father in law and mother in law are separated, but not divorced. We r having 3 floor house. 2nd floor is occupied by my mother in law. Ground floor is on rent. In 3rd floor we have only 1room, still we stay with our father in law. Now we are having space crunch, so we asked father in law to give us the ground floor. He is refusing to give us a single floor, neither he is letting us to lock our room. He by force wants to access our room. Is there any law, to stop him. D house is in d name of our father in law. I want to know can we legaly ask him to give our share or we have move out.