Registration of Affidavit for sale

My father and his sisters have a joint property which belongs to their parents, who passed away few years back. Now all sisters want to give the plot to developer but my father decided to take his share as cash instead of a flat. Initially we thought of selling the share to builder but then they decided not to register the plot to avoid any complications. We suggested to builder that we would sign a developer agreement but will relinquish our share of the flat by taking cash. Builder said that this will not be possible until development agreement is registered and a number allocated and plan is approved. Alternatively we suggested to include in the development agreement itself that we would take payment against losing our share of flat. Builder is suggesting that this kind of sale cannot be registered in development agreement. Could you please advise on this. Builder also advised that we, my father children, have to sign NOC. My sister lives abroad and she gave Indian affidavit (not from abroad), GPA. Builder is insisting that this be registered while my father is suggesting that this is not possible. Is it mandatory to register GPA locally in India.