Gpa - assitance

Dear Sir, My parents have been purchased a land during the year 1992. Please note the following: (A-PARTY : B-PARTY ---- C-PARTY (Dead not alive) : D-PARTY) A-party has sold to land to B party and it is registered ( I am having the copy of the same). B party has sold the land to C party through GPA. It is not registered or got any sale deed. C party has given to us (Dparty) through GPA which is GPA registered from sub register office. During 1992 up to 2002 it was under CMC and got Khata and extract. We have paid up to date tax and also BBMP Khata / Extract & PID in our name recently. Now I am planning to sale the land, but i am facing lot of problem from each and every one by misguiding me. I am really fed up of get hearing from each and every one The concerned customers are informing that the land has been got only GPA registration in Sub-register office and no registration has been done. We have paid all the taxes up to date and also betterment charges to the Government. Actually the customer are telling if you sell the land it will be registered in my name. But C party relatives comes and do any problem in future. You have to face it (D Party). One of the broker is telling that he is try to sell the land to one of the customer, Every one telling that it has GPA registered and there is no problem. Actual please note it is not GPA and it is GPA registered in sub register office and paid betterment charges and got Khata & Extract from CMC during 1992. Later the land converted to BBMP from CMC. I have given the document to BBMP and they have given me EC & Khata & Extract. Now we are trying to sell the land but the party & broker is telling that while selling the land it will get registered. They are telling we will look after the problems if it raise from C party. I am not able to believe them both party and broker. I want to go under legal terms because I do not want face any problem after selling the land and also in future. They are also informing that they will get the constent witness signature from the GPA son or wife. I am not able believe the words, they are bluffing and trying to CHEAT me. i informed them once you get the constent witness signature letter we will go for registration or else please give us in writing that if any thing happens in future the party will face the things under notary agreement. But they are telling there is an conditional clause that any things happen you have to come solve the cases. Please note all the records are in our name. I do not how to proceed further. please inform me that if i sell the land to the party and if party is ready to take the land. Is it possible that GPA person (C Party relatives or wife or son) can put case or do any problem to us during selling of land or even after selling in future. If so it holds good or bad. Please inform me how to proceed further immediately. PLEASE INFORM ME THAT AFTER SELLING THIS LAND TO OTHER PARTY AND HOPE HE GETS THE SALE DEED AND ALSO ALL THE RECORDS WILL BE TRANSFERRED IN THE NAME OF PARTY. AFTER SELLING CAN C-PARTY CAN COME AND FIGHT WITH US AND ALSO WITH PARTY. IS IT TRUTH. SO HOW I CAN CLOSE THIS DEAL. PLEASE SIR? Please also inform how to check the GPA registered in sub register office is Valid. Can I take any certified copy.