Must the tenant compensate the property owners for the difference in rent between the amount paid and the market value, especially if he is a university student and his father refuses to do so, and is it permissible to give charity with the intention of restoring rights to the rightful owners, the inheritors?

The old enduring lease contract, in which the term and rent are made perpetual, is void. The tenant is obligated to hand over the apartment to its owners upon their request and owes a fair market rent for the period he benefited from residing in it, as Sheikh Mansour mentioned in "Kashshaf al-Qina'." If the apartment owners absolve him of their right, his liability is discharged. Otherwise, he must pay them the fair market rent after deducting the named rent he already paid. If the tenant was the father, the son is not obligated to pay anything.