Demand of legal heir certificate by sbi for home loan

Dear Sirs, My Father and mother jointly had taken a home loan from State Bank of India, perumbavoor, Kerala in the year 2009 and bought a house in same area registered in my mothers name. Unfortunately, my father expired few months back. The account from which the EMI was being deducted for home loan was also jointly held by my mother and father and therefore EMI is being deposited to bank without any interruption till date. As the home loan interest rate had been drastically being charged more on us @12% (as compared to the prevailing rates of 10.1%), we approached the bank to reduce it to 10.1% by paying an amount of Rs 8000 as per existing bank rules. On intimating about my fathers death they demanded that a Legal Heir certificate has to be submitted to the bank in order to transfer the home loan in my mother 's name. Not only that me alongwith my brother have also been asked to be present in the bank for the transfer of loan formality. My doubt is that, in the event of death of my father, why do we need to transfer the loan to my mother's name when the loan was in joint possession of my father and mother? Is it correct on the part of the Bank to demand for a legal heir certificate? Will not a notarized affidavit serve the purpose? I need your valuable guidance on the legality of this issue. please reply. Waiting for your support