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

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

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?