What is the ruling of Islamic law concerning an oath of divorce in which one swore to refrain from writing any part of the inheritance to the heirs as long as he is alive? Is it permissible to write an apartment for the children and waive the rights of the spouses in it? And how can one expiate this oath?

If you swore by divorce, being aware of what you were saying, your divorce takes effect upon breaking the oath. Anger does not prevent its occurrence unless it was so severe as to remove awareness. This is the prevailing opinion of the majority of scholars (jumhur (definition)), which is used for issuing fatwas, contrary to Ibn Taymiyyah, who considers it an expiation for an oath. Swearing by divorce should be avoided.

Registering the apartment in the children's names, if it is a transfer of ownership to them during your lifetime, is a permissible gift (hiba), provided there is fairness. If it is after your death, it is a will (wasiyya) and is not permissible unless all heirs agree.