What is the ruling on the will written by the grandfather in which he favored males over females, and is it considered void due to the saying of the Prophet (peace be upon him) "No will for an heir"? And what is the ruling on the stance of the males who refused to divide the inheritance other than by this will?

A will in favor of an heir is not permissible unless the other heirs agree, based on the words of the Messenger of Allah, peace and blessings be upon him: "Indeed, Allah has given every rightful person his due, so there is no will for an heir" (narrated by Abu Dawud and others), and his saying: "A will in favor of an heir is not permissible unless the heirs wish it" (narrated by Al-Daraqutni).

Therefore, what the grandfather did by willing to the males and depriving the females is a great injustice and a grave sin. The heirs must invalidate this will and divide the inheritance as Allah Almighty has commanded; otherwise, they will be complicit with the grandfather in sin.