Depending on the amount to be settled, Bank may insist for indemnity, if all legal heirs authorisation for settling the amount in favour of your mother (NOC) and if the amount is more than Rs.50,000/- and if it is not a joint account, they may insist for succession certificate. Please contact the Bank with death certificate and there are more formalities required for death settlement depending on the religion of depositor.
RBI has issued guidelines in such matters and RBI gudilines have stautory force. You may go thru 'Master Circular on Customer services' Clause:19 & 20. The bank,IBA,BCSBI, prepares its policies in line with RBI guidelines. The bank has to maintain,display is,RBI, IBA,BCSBI,guidelines in Branch on its website and provide a copy without any cost to customer/claimants. RBI has guided that Bank may adopt procedures that does not cuae hardships to claimants. Depending upon threshold limit Bank may make the payment by getting the Idemnity,Disclaimer, surety in favor of mother. All other ClassI Legal Heirs e.g. sons,daughters shall have to sign.