What procedures should the banker adopt in opening and operating a joint account?

Can the balance in the joint account of husband and wife be paid to wife after the death of her husband?

Mr. Aman and Mr. Zaman have a joint savings account with your branch payable to either or survivor. Mr. Aman dies and his heirs claim 50% of the balance standing in the account. As a manager what step would you take in such a situation?