Land registration issue

Hi, My uncle passed away recently. He owns around 4 acres of fish ponds. This 4 acres is a single piece of land. This four acres of land is purchased 40 years back.But my uncle didn't registered them on his name. My uncle do possess only agreements. Of this 4 cares he got registered 1 acre on his name later. and rest of the 3 acres were unregistered. My uncle passed away recently. after my uncle demise my uncle's family friend came to my aunt and claimed that one acre that was registered on my uncle's name was sold to him in 2014. But none of my family even my aunt doesn't know about this. Even after 2014 my aunt does know only that all the land was still in their possession and my uncle is leasing out the 4 acres of land to some other person. The lease agreement was made by my uncle for the entire 4 acres of land(which also includes 1 acre of land the other person is claiming). In 2017 the person who took the fish ponds for lease was not able to maintain the pond and cancelled the agreement. After my uncle demise that person who took land for lease went to court claiming that my uncle didn't gave back the advance for lease. The person who purchased the land from my uncle did't took the possession. and no one is aware of that. Few of my family friends were saying that my uncle took money from him for interest and registered the land for him as part of shurity. That one acre of land is part of the complete 4 acres pond and cannot be divided. we were thinking The person who is claiming the land after my uncle's demise is trying to claim the land now instead of the money. No one is aware of that amount and even there we no promissory notes for that. He is trying to utilize this and trying to claim the land now after 5 years and my uncle's death. Even my aunt does't know anything about this money transaction or purchase. If it is a complete sale of pond he should have claimed the land and took the possession. So my uncle used to lease out this land completely on his name only. We got the registration papers that person is claiming and we noticed that registration was done as normal agriculture land instead of fish pond in the same survey number. I verified in AP Revenue and Registrations portal and looks like the registration the person was claiming was there in the official records as well. There is no possibility of dividing 1 acre of pond land as the pond land was one complete bit. Is this registration of that land was legal. and my uncle has minor daughter as well.