As per your query your father already sold the property to your neighbors through agreement of sale, firstly you have to find out whether it is agreement of sale or agreement of sale with possession. Secondly you have to observe whether it is registered agreement or not. Thirdly you have to see whether the Signatures belongs to your deceased father or not.
If the agreement is True :- It is your duty to get it registered by taking balance money from the agreement holder, since your father was executed the agreement when he was alive, he took the advance money from the party. Some interest is created on the agreement holder by taking advance money by your father on agreement holder. It is my advise you complete the transaction by taking the balance money. Even if your father is alive till now, he would do the same
If the agreement is False:- If you find that the agreement was not executed by your deceased father, if the said agreement is forgery, take immediate Criminal Action against your neighbors for cheating and forgery.
THE ROCKING LAWYER
V E MANOJ KUMAR
CELL NO 8686159292