Is this land and the structures upon it considered an inheritance from which the paternal uncles are entitled, according to Sharia, to claim their shares, or are they not permitted to take anything from it, bearing in mind that the father sent the money for the land and erected the buildings upon it, and it was registered in the grandfather’s name for fear of losing the right?

What you mentioned about your father registering the land in his father's name, fearing the loss of his right, is merely a claim that requires evidence, as the Prophet (peace be upon him) said: "The burden of proof is on the claimant, and the oath is on the one who denies." The advice, if you do not have evidence and your uncles do not acknowledge this claim, is to resolve the dispute through a reconciliation that preserves your ties and keeps you away from estrangement and discord.