All perfect praise be to Allah, The Lord of The Worlds, and may His Peace and Blessings be upon our Prophet Muhammad and upon all of his family and companions.
Sharia has legislated making a bequest as a window of opportunity for the person who has failed to make donations to charity; however, there are certain conditions that must be met in this regard; some of them are:
First: The bequest must be restricted to one third from the deceased`s estate unless the heirs approved of more than that, as indicated in the following Hadith: "(Give) one-third, and one-third is a lot. It is better to leave your heirs independent of means, than to leave them poor and holding out their hands to people." {Bukhari&Muslim}.
Second: Making a bequest to an heir isn`t permissible unless the other heirs had approved of it, as indicated by the following Hadith: "I heard the Messenger of Allah (PBUH) saying: "Allah has appointed for everyone who has a right what is due to him, and no bequest must be made to an heir." {Abu Dawoud}.
Third: The bequest mustn't violate the principles that Sharia has set for the division of the inheritance; therefore, it isn`t permissible for a given person to bequeath equal shares to his male and female heirs, as this violates Sharia texts. In conclusion, a bequest that violates the rules of Sharia isn`t valid, and the one who makes it as well as the one who executes it are considered sinful because they have violated Sharia and led others to take unlawful wealth. Division of a person`s estate is permissible only after his/her passing away, and it isn`t permissible for a son to ask his father to divide his estate while alive because it is his own and no one is entitled to it other than himself. Moreover, wealth is called an inheritance after a person passes away.
Al-Khateeb Ash-Shirbini said: "There are four conditions for an inheritance. The first is the death of the inheritee." {Moghni Al-Mohtaaj 4/10}.
Also, asking one`s father to divide his wealth while alive is an act of unkindness on the part of the son and violates the injunctions of Allah as far as treating parents is concerned. And Allah knows best.