Death Certificate

My grand father purchased a property in a public auction in 1954 after 65 years some people claim to be the grand sons of the defaulter(ex owner) and claim that the father of the the defaulter was alive at the time of degree and auction and when father was alive son can not become owner as the land was purchased by his father, they claim with a death certificate of father who died in 1966. The defaulter him self written a registered deed of mortgage claming he become owner after the death of his father and his name was in the motation of the property at the time of auction is there claim legal . it comes in civil or criminal please advice