What is the ruling on a document written by a grandfather to وقف (endow) his property for his two grandsons, to the exclusion of their deceased father and their paternal aunt, and on the condition that it be for males only among their descendants?

If the grandfather endowed all his properties for his two grandsons and their descendants during his lifetime and sound judgment, then the endowment is valid, and his properties become an endowment for them, excluding the paternal aunt. However, if he wrote this as a will, and if the descendants were not in existence at the time of the testator's death, then it is void unless the heirs approve it, due to the hadith: "There is no will for an heir." If the descendants were in existence, one-third of the wealth is divided between the two grandsons and their male descendants; thus, the two grandsons inherit it, with the paternal aunt sharing in this inheritance, and it becomes an endowment for the descendants. This issue is known as "awlad al-a'yan" (children of specific individuals). The division is subject to nullification by the birth or death of a grandson or a member of the descendants. The remaining two-thirds are an inheritance for all heirs. The questioner is advised to refer to the Sharia courts in case of dispute regarding these matters.