Clarity Regarding Family member Certificate

My father has a family dispute with my grand father(along with his wife, 2nd son and 5 daughters). My grand father got expired in 2012 and remaining family members didn't get Legal heir certificate because my father made objection for it. So they didnt get legal heir from 2012. Recently my father got expired and now my grand mother along with his 2nd son and 5 daughters are trying to get legal heir because my father is no more for objection. Initially they opted for Family Member Certificate at MRO office and MRO is willing to issue family member certificate for my grand mother stating my father(i.e., applicants 1st son) is expired recently. I went to MRO and asked for the same not to issue Family member certificate to my grand mother. I asked MRO that we (My mother, Myself and my sister) will be legal heir's for my father, so asked MRO not to issue Legal heir to my grand mother without our approval. But MRO denied my request. What kind of right do i have to stop the FMC to my grand mother. Can MRO issue the certificate to my grand mother stating my father has died ? or My mother, myself and my sister's approval is required to issue the certificate ? Please help me on it, i am in need of it