Land dispute after 45 years by ex serviceman's son.

my grand mother bought land from ex serviceman at 1965 he was allotted 10 acres of land from madhya pradesh on account of retired serviceman. he sold that land to my grandmother, and he stated on registry papers that "i am buying land at different location,as this land is not suitable for me, hence selling the land" after 45 years, son of that serviceman has sued us, stating that, land given to ex serviceman are non transferable in nature. we are very confused, as my grandparents are dead, as well as that ex serviceman, i want to know that is there any risk for us, and guidance