How is the waqf distributed among sons and grandchildren, taking into account the waqf text: "To my parents, then to their children, and then to their children," and given that there is a deceased sister who has heirs, and a deceased father and a living mother?

If your father's share of the endowment consists of two apartments, you may either utilize them through muhayat (alternating occupancy) or rent them out and divide the rent equally among males and females.

The direct children of the endower (male and female) benefit equally from the endowment until the death of the last one of them. Then, the benefit transfers to the children of the sons only, excluding the children of the daughters. This is because the children of the daughters are not included in the term "walad" (child/offspring) according to custom, language, and Sharia. So, if the endower states, "for his walad," it includes his children (male and female) equally, and then only the children of his sons, as supported by the Almighty's saying: ﴿Allah instructs you concerning your children: for the male, what is equal to the share of two females.﴾