What is the ruling on the custom that requires daughters to waive their inheritance after the father's death, and are the males who take the full inheritance after their sisters waive it out of shyness and courtesy considered sinful?

It is not permissible for brothers to insist that their sisters waive their inheritance rights to them, especially if this is done out of shyness and courtesy, as it then becomes close to coercion. Allah has granted daughters their right to inheritance, as He Almighty said: "Allah instructs you concerning your children: for the male, what is equal to the share of two females. But if there are [only] daughters, two or more, for them is two thirds of what he left; and if there is only one, for her is half." Also, the Prophet, peace and blessings be upon him, said: "Indeed, Allah has given every rightful person their due right." A daughter is more in need of inheritance due to her vulnerability. This action is not permissible, and it is not correct to exploit women and take their share, even if it is in the form of a non-voluntary donation.