What is the ruling on a father selling half of the land granted by the state, knowing that he does not own it and that its sale is not legal, and does the buyer have any right to it, and does the father incur sin for selling what he does not own?

Your father did not have the right to dispose of the land by selling or renting it out, as this contradicts the state law that authorized him to benefit from it without ownership. Selling and renting are branches of ownership. The fundamental principle is the obligation to adhere to the condition, based on the saying of the Prophet, peace and blessings be upon him: "Muslims are bound by their conditions." If the buyer knew that the land was not owned by your father, he should not have bought it, because buying it would be cooperating in sin and aggression, as Allah Almighty says: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression." As for how to end this dispute, it should be referred to the judiciary.