Tracey Brooks

My father died last year at the age of 88 which i only recently discovered via his grave when visiting my grandparents grave. You may ask why i have only just discovered his passing, where was i. The answer is extremely personal and there are valued reasons for the lack of contact. It appears by law my sisters and i are valid next of kin and wish to pursue the following avenues. I have discovered that there was no will, that he had a post office account where he would have possible received his state pension. The funeral and clearness of house was handled by his sister, claiming she was the only relative. My question is; Am i able to make contact with i suspect the DWP directly, If so, what would i need to produce as proof ? this is about his state pension for info of exactly who closed his account etc after his death. Any links or contacts would be gratefully received. Thank you.