What is the ruling on a father's will to allocate one-third of his estate for the education and marriage of his children until the age of thirty, and is it religiously obligatory to act upon it?

If the will stipulates selling one-third of the real estate to spend on the children's education and marriage, then it is a will for an heir and is not enforceable unless all heirs agree, based on the Prophet's (peace be upon him) saying: "There is no will for an heir."

However, if the intention is to rent out one-third of the real estate and spend from its rent on the children's education and marriage, then this is a permissible and valid endowment (waqf) and should be acted upon.

Similarly, if the real estate is to be sold and one-third of its price is invested in an endowment for spending on the children, then it is a valid temporary endowment that will eventually revert to the inheritance.