Property acquired

Hi, I would appreciate your advice on a property dispute on behalf of my father. My father owns two properties in india. He lived in one property with my mum and us two sisters. He alowed his parents, 2 brothers and thier familes to live in the second ( in 1983 or so). Reason being both his brother did nothing for living. his youngest brother (3rd)was alcoholic, my grandfather diSowed him,he left that property around 12-13years ago, while his wife left him and lived separately in a different city. My father parents , one brother (2nd)and his wife died -they had a daughter who now lives with her aunt ( wife of disowned brother). The property is registered on my father's name. However because of daily quarrels and mental harassment by his father, my father 35 years ago wrote on a plain paper that" I sell this property to my father in some thousand rupee" and signed it. This paper was never got registered on stamp papers. As on today's date the registry of the property is on my father's name. My father locked this property asThe property was empty after 4 family members died, one brother left his wife ( indu) left. Now while my parents came to visit my family in London, this lady indu broke in to the property and started living in it. Moreover she even rented out one of the floor. And claims that she has legal right on the property only because my father signed the property on my grandfather name. Not sure if I have explained the issue clearly but your guidance would be highly appreciated. Family compromise is not the option we are considering.