Bank account nominee

My father in law owns a bank account with a very large amount of money. he lives with alone because my wife and other five sisters lives separtly. He was very old and in very poor health. Due to pressure from my elder sister in law, He designated him as the nominee on the bank account. It is his wish that after her death the money in the bank account be divided equally between all six sisters. But she also worries that my elder sister in law will just take all the money and not give us anything. He has registered his will. I am also worried that after my father in law death, my elder sister in law will simply take control of the account and electronically or otherwise transfer all the money to his account. I understand that there is a recent Supreme Court decision prohibiting a nominee from owing all the money and that a nominee's role is merely to distribute the money to all legal heirs. However, if my sister in law takes all the money, I would have to go to court to get it my share which could take many years. What can I do to prevent my sister in law from taking all the money after my father in law death? I and four sister in law give application to bank and post office not to disburse this amount.