Nomination in bank accounts

Hi my bua is Nominee in most of the bank accounts and a locker of my grandparents. I somehow got her on table to negotiate. Basis the negotiations, My dad, chacha and bua gave a joint letter to the banks in September 2020 that they 3 are legal heirs and the accounts of the deceased can be operated jointly by all 3 only. Also, My bua , my dad and my chacha signed a notarized affidavit in oct 2020 that all Money and assets belonging to my grandparents shall be distributed equally between all 3 (dad, chacha and bua). Now bua seems to be backing out and I suspect she will claim all nomination in her name including bank locker. My question Can I stop bank from disbursement of nomination money and locker to bua on the basis of: 1. Bua herself submitted a joint application (along with dad and chacha) to bank in sept 2020 stating that they 3 are legal heirs and shall access the accounts of the deceased jointly only. She had physically attended bank with my dad and chacha to submit this application. 2. While submitting this application, I ll also attach the notarized affidavit signed by bua, dad and chacha. Basis these 2 things, can I stop bua from claiming her nominations. I m vary concerned about the locker because no one knows its contents