What is the ruling of Islamic law regarding a man's bequest of two apartments from his estate to his grandson (son of his son) and his granddaughter (daughter of his daughter), given that his son refuses to carry out the bequest to the daughter's son, and knowing that the bequest is within the limits of one-third (of the estate)?

A bequest to a non-heir, not exceeding one-third (of the estate), is a valid and enforceable bequest. The heirs do not have the right to reject it, and it becomes binding upon the death of the testator and the acceptance of the legatee. If the heirs refuse to execute the bequest in this case, they are sinful, and the legatee has the right to refer the matter to the Sharia (definition) court. However, if the bequeathed amount exceeds one-third and the heirs do not permit it, only one-third of it shall be executed, and the legatees shall divide it according to their respective proportions in the bequest.