Is it permissible to relinquish a plot of government land to one of the brothers after he has paid the fees and one of the brothers has given his approval out of courtesy?

If the land was granted to the siblings at a price lower than the market value, and everyone relinquished their share to the brother who paid the fees, then there is no harm in that if they were adult and mature. As for whoever refused, or accepted out of shyness, they must be compensated for their right, or they should keep their share and pay their portion of the fees; according to the saying of the Prophet, peace and blessings be upon him: "The property of a Muslim is not lawful except with his willing consent."