How is the apartment's price divided between the son and the daughter after the grandfather and wife waive their shares?

The waiver by the deceased's father and his wife of their share of the inheritance in favor of the deceased's son and daughter is considered a gift (hibah). This gift is to be divided among the recipients according to the donor's wish.

If the wife is the mother of both the son and the daughter, she must be just between them in the gift, by giving the daughter a share equal to that of the male.

As for the grandfather, he is not obligated to be just between his grandchildren in giving gifts, but it is recommended for him to do so. Therefore, the deceased's father should divide his share of the house equally between them.