Is it permissible for paternal aunts to claim ownership of land designated for males after twenty years have passed since the death of the grandfather and father, knowing that the grandfather had stipulated that the produce of this land was for the daughters as long as the grandmother was alive?

It is permissible for a person to distribute their inheritance during their lifetime among their heirs as a gift, and they must be just among them, giving the male twice the share of the female.

If a father favors some of his children over others in a gift, it is either with their explicit consent while they are adult and rational, in which case there is no harm, or it is without their consent, in which case he has acted unjustly and oppressively.

If the grandfather passed away and your paternal aunts did not explicitly consent to the favoritism, then the land must be re-divided among all heirs justly, with the male receiving the share of two females, even if the favored one died before justice was served.

Consideration should be given to the reason for your paternal aunts' delay in claiming their rights. If there is a valid reason, the division should be redone. If there is no reason, it appears they have consented. However, if the males know that their sisters have never consented, then they must re-divide the inheritance.