Pagadi System

My father had bought 180 sqft room Ground Floor in Khar in 1993 on the Pagadi system. Some years later the landlord sold the entire building to someone else and the same process of pagadi system is being followed by us for many years. My uncle used to stay in that house for some period now he has left and we stay in that house. Now the building is very much old and not stable, It can fall anytime. The building has only two tenants one of which is us and another family. Recently the builder had approached for the redevelopment for the property and at the time of discussion the landlord says that if the property is constructed of 3 floors he will not give us the same ground floor and he will give the room at 3rd floor. My father is a heart patient and he cannot climb the stairs. Second thing is due to the bad condition of the building the landlord has got himself shifted to some other place to reside nearby which was arranged by the builder. The same was done with the other tenant after some time. Now only we are stuck and the landlord is trying to give us problems of all kinds. We also asked the other tenant that how u managed to get these things done but he doesn’t answer and is not helpful at all. What can be done in this situation? Please I would be very happy to receive some advice as my father is not that much literate and I am the only son who has to look after all these things. What can be done so that we could also get ourselves shifted by the builder to some place safe.