Does my grandfather has right to keep the property?

Person “ A” has two sons A1 (elder ) and A2 (younger ) {Hindu undivided family}. Government distribute free land in the name of elder brother A1 1936. A1 has 5 children. First child of A1 made Kata(ownership right) in his name in 1963 and sold that property to third-party 1. In the same year third-party sold the same land to my grandfather (third-party 2) in 1991. We are cultivating this land from 1991 to 2020, but any of the members from protested or filed case against us in any court till 2012. In 2012, second wife’s son of A2 filed a equal share and in justice to his father A2 by A1 case against of A1’s all 5 Children. In the plaint sheet he mentioned A1’s children as defendants and included my grandfather purchased land survey number but he didn’t made us as defendants. He didn’t send us court notice till now(2020). Is it my grandfather’s claim over purchased Legal? Does A2’s case stand in the court? He is not coming for negotiation, what can I do? Please help me in further steps.