1. Nominee is only a custodian and and in view of nominee's death, to equally distribute the proceeds to all the legal heirs, if there has been intestate death of the bank account holder. However, if the account holder had specified through WILL, then it will go to the beneficiaries as stated in his WILL.
2. In the instant case, as per your narration, your grandfather, grandmother and your uncle ( father's brother ) have died intestate ( without executing a WILL ), then the entitlement to the share of all movable (proceeds in bank account, car, jewelry, etc.,) and immovable properties gets divided into their children, viz., Sister and 2 brothers (Your father and uncle, who is no more), i.e., 1/3rd share each. In view of your uncle's intestate death, his 1/3rd share will be further subdivided equally to his wife, daughter and son. Now the sister, your father, your uncle's wife and 2 children can claim the proceeds in your grandfather's bank account.
3. The property gifted by your grandfather to your uncle has been done during the lifetime of your grandfather and your uncle and the gifted property naturally being the self acquired property of your grandfather. However nothing prevents you from disputing/challenging the Gift Deed.
4. Since the property which your father is living in belonging to your deceased grandfather, and your father's sister, your father, your uncle's wife, her daughter and son are entitled to share in the property. However to stake a claim in this property, your father's sister, your uncle's wife and her 2 children have to execute a registered Release/Relinquishment Deed relinquishing their individual entitled share in your father's favour in the jurisdictional Sub Registrar's Office. If it's done, then your father can stake a claim in the house in which he is presently living.