Father's property bought in Grandfather's name

My Dad had purchased some agricultural land in Bijapur (Karnataka) in his father’s name in 1980. My Grand father & uncle were very poor to buy any land, hence as a prestige my Dad had kept it in Grand father's name, who died in 2000. Then my elder uncle had managed to get illegally transfer one of these property in his son’s name & other in his wife’s name by forging my grandfather’s thumb impression & without registering it. Now he says that my grandfather had gifted them & has incorporated his son & wife’s name in 7/12 documents, probably through collusion with some panchayat members. There is no Will or Gift deed & none has been registered with the Tashildar or any other authority. My uncle also knows that he had manipulated & done wrong things, hence use to say that he will discuss the issue later with my Dad & return his land back. But that day never came. Now my father want's his land back in his name. Please advice the procedure? So let us know how to reclaim this complete land in my father's name, who had actually acquired it through his own funds. Please update on clauses / legal aspects for it.