Claim on Ancestral Flat

My grandfather (Hindu) made 4 parts of his flat and paid my father money as his share and my father left that flat. 3 shares left were of grandfather, his wife and second son. He allowed second son to stay in that flat and left for native place. This was some 20 years back. My grandfather and his two sons are no more. Do I have right on that flat? Specific Information: - Flat belonged to my Grandfather when share was given to my father. - I am not sure whether the said flat was later transferred in the name of second son. - A few relatives were called upon and my father was asked to submit in writing that he would have no claim in said flat in future. The same was not on a stamp paper or ever registered. - As the market value of flat was divided in four parts and one part was given to my father, the second son eventually got 3 shares as he stayed in said flat. Both grandfather and his wife passed away later. - Can I claim share in these 2 parts (Grandfather and his wife).