Case filed seemingly to extort money against our land.

Summary of the matter. We have half a hectare piece of land in our possession for past 57 years we have been doing farming on the said property and now we wish to sell it off. All the legal documents have our names on it. Our ancestors have bought the land from someone named Pathare and the sale deed was executed in 1967. Now, Pathare had bough the land from someone named Pawar. Their sale deed was executed in 1964. Now, 3 people in Pawar family signed the document. Between those 3, 2 were adults and 1 was a boy under 18. His mother has signed the agreement. The one whose mother signed the agreement and the mother both are dead today. The said person has been dead for 14+ Years. Now the children of this person have filed a case saying, our grandmother signed the document without our father's knowldge. Does this case hold any water? We have been fighting it and we have filed to dismiss the case under 7-11. Please suggest weather should we sell the land to a builder or not? Will he face challenges while selling flats on such property?