Do the two apartments gifted to the mother, which are considered the shares of the two sisters, fall under the estate of the deceased father, or are they considered an independent gift from the mother?

What the father gifted to his wife and she possessed before his death is considered her private property and does not fall within the inheritance, and she has the right to dispose of it. If the mother wishes to divide the property among her children, she must be just in their division. It is not permissible for her to gift the males without the females, and she must give the female the same amount she gave the males, or half of what she gives to the male, because the mother is like the father in the obligation to be just among children in gifting. As for what the father left behind, it is divided among all heirs according to their legal shares, and it is not permissible to deprive the female of her share in her father's estate, unless she willingly waives it.