Does my deceased father have a right to his uncle's land, which turned out to be agricultural reform land and not owned by a government entity, after the deceased grandfather divided it between them?

If the reason for the payment of money to the uncle is proven to be erroneous, then the heirs of the deceased have the right to claim it back, because their inheritor paid the money based on a mistaken premise. They have the right to reclaim the entire amount. The heir succeeds the deceased in matters of wealth. So, if the father paid the money based on the assumption that the land belonged to the state, and the opposite was proven, then the heirs have the right to re-distribute it according to the correct reality.