Land dispute

My dad(late) bought a land in 1985. Now that land is disputed as double entry by an opponent who is saying that his father is the owner and filed a case against us that we illegally occupied the land. Even though we misplaced the original doc,still we won the judgement in Oct 2013 in our favor just with the the duplicate pathra(which we applied and got) and also EC which is under my dads name since 1985. But now wen we thought to sell the land the opponent is now showing a photocopy of a original pathra registered in his father's name(which he failed to produce in court) saying that he too enjoy the right in this property and claiming 2/3 of the selling price. As its 1975 pathra it is not computerized,where each page has a different month seal (jan ,july & Mar 75) looks fraudulent(He had shown us only xerox,refused to show us the original copy so far). Adding to that, while selling the land he is not attaching his land pathra's copy instead he s keeping his mother's settlement as a proof disrespecting the courts judgement,so that to bring his name behind us in EC(since 85 our Dad's name is in EC). At the time of drafting He is dividing the 8.25 cent' land into 3 different plots (~2.68 cents each) and asking us to sign in all 3 documents,so that to have three new pathras after selling . Seeing this ,we smelt something fishy and had postponed and stopped the process meantime. What should I do,even its so evident that we (me,My mom and a sister) are owning the land,the opponent is not allowing us to sell and stopping all the ppl frm buying the land. At the same time he couldnt able to sell the land without our signatures too.....How will I deal or claim our property??.....Or we agree with our opponent and sell the land considering it as double entry,can we claim half-half? or will that "predate pathra person" will get more share??.The land value is 24 Lakhs .Hw much we should get if we sell it in the cause of double entry reason?