What is the ruling on the religious books inherited by the father and uncle from the grandfather, in which the grandfather stipulated that they are an endowment (waqf) for his children and their descendants who are students of knowledge, and are these books considered an inheritance for the children after their father's death?

The stipulations of thewaqf (endowment) donor must be followed, so long as they do not contravene Sharia (definition). The stipulation of the donor is like a stipulation from the Lawgiver (Allah). Your grandfather stipulated that the books are an endowment for the scholars among his sons and their children. If there are scholars among you or your cousins, then you share with your uncle in benefiting from these books. If there are no scholars among you or your cousins, then only your uncle benefits from them, provided your grandfather's condition applies to him. If the waqf donor did not specify a beneficiary after those he mentioned, then if the person to whom the condition applies dies, it becomes a waqf with a severed chain of beneficiaries. In this case, it reverts to the heirs of the waqf donor, as an endowment for them, according to their shares of inheritance. It remains an endowment, and they do not own the right to sell or donate it.