Partition of ancestral land

Hello All, I am looking forward for some advice on a property case due to which my family is suffering. My grand father and grand mother hard worked and own 15 bheega (5 acres) agricultural land. They have 4 sons and 2 daughters. Now, one son got himself a pavati (written notary) saying that with father and mother's consent 6 bheega is given to him as gift. He has his father's (my grandfather's) thumb print on it. At that time he agreed to take care of my grandmom so all the brother's and sisters gave consent too. However he never took care of grandmom nor gave any compensation. Que.1 : Are my grandmother's thumbprint also required to make it legal as it was my grandmother's hard earned property as well? Now, remaining 9 bheega was then divided equally between 3 brothers and the daughters were given dowry/house at time of marriage (1970's) But recently, the son who got 6 bheega land as gift claims that since he didn't get any property in partition he should get a share in that 9 bheega land. Also he called one of the sister to put a claim for the land. There is a pavati(legal document) for partition deed available with three brothers. One of the three brothers already sold his share which is 3 bheega out of 9 bheega. Now remaining ancestoral land is 6 bheega land. Que.2: Do my uncle who was gifted land already and the aunt who was given dowry has right to claim the property? Que.3: If they have the right to claim, then it means they should claim against the original 9 bheega jameen or remaining 6 bheega jameen? Que.4 If they should claim out of 9 bheega jameen then can my father file a claim of quiet title for atleast 9 bheega/ 6 sons & daughters = 1.5 bheega jameen? Or if 6 bheega then a quiet claim for 1 bheega jameen?? My grand mother is alive and living with my dad with no support provided from any brothers or sisters. Please advice. Many Thanks in advance.