Is the supplicant obligated to fulfill his promise to his friend to donate part of his liver, despite his wife's refusal and her fear for him and their children, and would he be sinful if he were afflicted with harm because of that, and does his wife have a right to participate in this decision?

It has been previously established that the preponderant opinion regarding organ transplantation from living donors is permissibility, provided certain conditions are met. If you fear harm to yourself as a result of donating a part of your liver to your friend, then there is no blame upon you. However, if trustworthy doctors advise you to donate without harm, then rely on Allah and donate to him. And if any harm befalls you after consulting the doctors, there is no sin upon you from the perspective of your children. It is not among the rights of the wife to be consulted in such matters, but it is preferable to consult her to appease her and strengthen the marital relationship.