Builder not keeping his promises

My grandfather was lawyer by profession and had bought multiple properties in Pune. He had 2 sons and 4 daughters. When my father was around 9-10 years old, he lost his father. Since then my uncle didn’t give my father a penny even though he was earning rent from all those inherited properties. Some years ago, my uncle died. Our family was living in 1RK in one of the grandfather’s property. After my uncle’s death my cousin has started redevelopment of that vada. He mentioned built-up area in agreement, and we didn’t consult any lawyer and we didn’t know difference between carpet area and and built up area when we signed agreement for redevelopment. So we didn’t say Anything. Along with builder He made my parents vacant their house before all the tenants, still we didn’t say anything. In August, builder agreed to sell us a car parking in 3L plus 1.5L for maintenance. Even after following up He Has not given this in written yet. Now he is not paying us the agreed upon rent too. My parents are not earning since last 5 years atleast. My brother is still in college. I am bearing all the expenses for all of them since last 7.5 years.. I want to know can we do something legally so that my parents don’t need face all this Harassment when they are already in their old age.