Should property be purchased which is owned by 2 brothers ?

I purchased a land in Hyderabad in 2004. the original owner inherited a land of 4 acres from their father to 3 brothers. They sold 60 plots breaking the 4 acres to different parties, we are one of them. Currently I want to sell my property but now it has come to the attention that only one brother has signed the sale property for all 60 plots and all properties are not legally cleared. Now when we want to sell the property the brothers are asking us to pay 6 lakhs so that the other two brothers can sign and clear the property for us to sell. After 14 years the original brothers owners are asking 6 lakhs from all 60 plot owners when they are selling for clearance. The party who want to buy from us have given an advance of 10 lakhs and we have signed an agreement stating that we are going to sell to them. If we now withdraw, due to the exorbitant demand of 6 lakhs for clearance then they are threatening to go to court. my Religion:christian What can we do in this case.