All perfect praise be to Allah, The Lord of the Worlds, and may His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
In His Glorious Quran, Allah, the Almighty, Has Clarified the rules of inheritance and Has Given each person their due share, and this division is neither open for interpretation, nor addition or subtraction. He, The Exalted, Said (What means): "God (thus) directs you as regards your Children’s (Inheritance): to the male, a portion equal to that of two females" {An-Nisa`/11}.
In light of this, a Muslim isn`t at liberty to violate this divine rule by giving equal portions of inheritance to males and females. Accordingly, the bequest mentioned in the above question is invalid, so it mustn't be executed.
However, if all the heirs agreed to dividing the estate on equal basis among themselves, after the death of the testator, then that is permissible because they become entitled to their shares after the death of the testator. By doing this, heirs who received extra shares have donated them in favor of those who received lesser ones.
As regards the bequest made in favor of the daughter who had passed away before her father, it is considered valid and must be executed. Accordingly, that portion must be given to her son if he chooses to accept it and according to the manner stipulated in that bequest. This is provided that that portion doesn`t exceed one third from the estate. And Allah Knows Best.