Father not giving any rights in the property

My grand mother had purchased a property in the name of my father when he was minor.Father was just a student at that time.Grand mother didn't had income that time. The amount came from our grandfather shop he had 2 daughter and 2 sons.My father had paralysis attack 20 years back. My sister with evil intention wants to sell the property they have managed to brain wash my father against me. The only reason is that I have refused to divorce my wife. My sister's has problem with my wife who belongs to poor family and sisters think she should not get property who has not brought any jewels or dowry in the marriage and belongs to poor family. They already have managed to sell our all ancestral agriculture land by brain washing my father. Now they want to sell two houses in single plot of which one house is in my possession . I need your help to protect this house. I have already spent my life in upbringing of my both sister's and taking care of my parents and now I have no resources left with me. Please guide me in this issue.