All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
The gift that your grandfather had assigned from his property to only his daughters, apart from his sons, was contrary to the justice that Allaah The Almighty and the Prophet, sallallaahu ‘alayhi wa sallam, commanded to observe. The Prophet, sallallaahu ‘alayhi wa sallam, was reported to have said, “Fear Allaah and be just between your children (when gifting them)…” Hence, justice in giving gifts to one’s male and female children is mandatory according to the jurists’ sound opinion. A father is not allowed to give preference to some of his children over the others unless for a sound reason. If he gave preference to some of them over the others by, for example, having assigned gifts to only the daughters as your grandfather has done, then he must rectify that by either withdrawing his gifts or giving gifts to his sons in a manner that establishes justice. This is according to the Hanbali school of Fiqh. To do justice is to either give each male twice the share of a female as normally done in distributing inheritance, or to give an equal share to both male and female. These are two opinions by scholars.
On the other hand, it is true that a Muslim is required to leave a will, and the will could either be obligatory, recommended, or disliked. There is no contradiction between legislating the will and distributing the inheritance, since a will that is Islamically valid must not be made for the inheritors. Rather, it is recommended for a person leaving behind a large wealth to assign less than one third of his wealth to charitable acts or to his needy relatives other than his heirs, and the like. Finally, it is mandatory that a person leaves a will if he is has debts and rights (that need to be paid off).
For further information, please refer to Fataawa 95614, 96941 and 85091.
Allaah Knows best.