Bank loan closure and release of documents

Sir, i am ramesh, from hyderabad, me as a co-applicant and my father as main applicant taken a housing loan in the year of 2005, from sbi, and in 2008 eight my father passed away, due to heavy loss in business i couldn't able to pay regularly my emi's eventually our property came under npa. later bank people knowing that my father is no more, send us(1. me(as co-borrower)2., my mother, sister(married 18 years back) 4&5 my younger brotherslegal notices collecting my father death certificate and my mother's family pension papers(my father retired as a state government employ) where we all legal heirs are mentioned in those pension papers(we have not taken any legal heir certificate or family member certificate). we paid all our dues including of every charge, but the bank people are refusing to give documents, asking for legal heir/family member certificate. is this a genuine reason for not releasing the documents?! where we are legal heirs for payment but not for collecting the documents!!!