Are the funds that the father gifted to his mother after his death considered her property to dispose of as she wishes, or must they be divided Islamically among the daughters and the father's siblings?

The fundamental principle in dividing a father's estate is that it should be distributed among all heirs according to the prescribed legal shares. Any claim of a gift or debt against the estate requires legal proof. A father's gift to his daughters or wife is not valid if it was made during his death sickness or if he did not take possession of the gifted property during his lifetime; in such cases, the estate is considered property to be distributed among the heirs. If he did take possession of the property during his lifetime, but the father was in his death sickness, then it is considered a bequest (wasiyyah), and a bequest to an heir is not permissible without the consent of the other heirs. A father's spending on his brothers or a mother selling her gold to spend on her husband's family does not justify monopolizing the inheritance; it requires legal proof before the court, otherwise, the property is an estate to be divided among all heirs.