How to transfer FD if mother has died without declaring any nominee

Dear Sir, My late mother posses Post office FD (MIS) in her single name without declaration of Nominee. She was dead in the Mid Month of January 2017 and later we have found her FD. We went several times to Post office to claim the said FD and encash / Cheque into her / our favour sons (Ours). Eventually they rip our orally and finallly our case was about to hear They have asked several documents to be process under as follows : 1. Two witness to be brought with Aadhar card and Pan Number. 2. Two Surety from Govt Institutions / Banking Officals. 3. Two more Witness from the above Point No.2 4. Death Certificate 5. Indeminity Bond 6. Notrary We appeal to Post Office who is in Office in bearer that except with the Point No. 2 (Surety) that would be difficult from our side because we do not know anyone in person but they insist to be done from our side. Our matter is became halt and remain unbalanced in due course in our said case so we decided to consult a Legal advice