PATTA NAME REMOVAL WHICH IS EXISTING AS JOINT PATTA With PRE-Owner

Religion-Hindu Sir we have purchased a land 20 years back. Still the property patta exist has joint patta with previous owners fathers and his grandpa name in patta (both expired before the purchase of the property) along with my parents name. When we approached V.O with original property bond which is completely signed by previous owners 5 descendent Childrens, still the V.O is asking for Legal heir certificate and V.O also added without legal heir certificate he cannot give approval for name transfer. When we approached one of the previous owner’s son, who is a retired Tahsildar of the same town said, he don’t posses any copy of legal heir certificate. And he has also threatened me and said he is willing to purchase the land at the same cost for what we have purchased from him 20 years. Need your valuable legal advice in removing previous owners name from Patta. And can my previous owner can take my property from me, even after signing the document.