Since the possision is not handed over,the question can be raised on sale deed,as Under Section 54 ,TPA,the delievry of posseion matters.
You are in in possesion means you have a right to stay in possesion only the transfer of title has taken place. The property is ansestral and belongs to your grandfather so all the lgal heirs can claim share. You can negotaite but for that you need to bring them on table by challeneg the sale deed.
At worst you can claim a right for being in possesion, until the matter is not solved don't lose the posseison. You need to file for suit for partiton, like that you can bring under pressure all of the parties to rerach any agreement.