How can i get my fathers death certificate.

My father died recently in Kolkata and he was a central government employee. I am the only child and me and my mother stay in Bangalore , after my father death I am not getting death certificate of him and bank papaers, PPO book from his brothers. Now my mother has to submit all these in bank for getting the pension. But I don't know how I will go ahead. Kindly suggest me how to go ahead for this case.