Property matter

My father and Uncle (father's elder brother) had jointly purchased a flat and the agreement is having both names in the year 1966. The share certificate is showing only my Uncle's name. Both the brothers have expired. The conveyance deed of the society is showing both names. Now the society is denying the right of half ownership to my mother. The society says that they will consider the name mentioned in the Share certificate only .The Society has transferred the share certificate in the name of my aunt not taking into consideration the names in the Agreement and Conveyance Deed. The original agreement is with my Uncle’s heirs and not showing to us or to society. How can we prove our right in the flat? The flat is presently occupied by uncle’s family. On what basis society can refuse the right of membership to us as there is name in conveyance deed and funds were contributed by my father also. We had applied to Sub registrar under sec. 22/23 for membership but was overruled by sub registrar on grounds that original Agreement of sale be produced.He did not ask for any documents from the society or the heirs of my uncle. Can he do this? The sub registrar didn't took into consideration the name in the Conveyance deed of the society. Now the building is under going process of redevelopment and the developer is finalizing the agreement with the uncle's family. What can be done to stop the redeveloper from doing agreement with heirs of my uncle. Are we not having legetimate right of 50% ownership of the flat.Please advice as to what should be done.