Is it permissible to allocate a portion of one's property to a son during the father's lifetime to help him support his sisters in the future, and can this be done through a will after the father's death?

It is not permissible to single out the son with a gift of money to the exclusion of the daughters, because Islamic law requires justice among children in gift-giving, as the Prophet, peace and blessings be upon him, said: "Fear Allah and be just among your children." What was mentioned about the son's future responsibility for his sisters cannot be asserted with certainty, and شرعي (Shar'i) justice should not be violated for the sake of future conjectures, as the brother might oppress his sisters. It is not permissible to write wealth in the son's name as a bequest to an heir, except with the consent of the other heirs. The advice is to leave the matter to what Allah the Almighty has legislated, by dividing the inheritance among the heirs according to Shar'i law after death, to guarantee the rights of the daughters.