Is it permissible to sell a portion of a disabled brother's land for his needy brother's surgery, with the consent of the mother, who is his guardian?

It is not permissible for the guardian to dispose of the minor's wealth except in what is most beneficial for him. It is not permissible to donate from his wealth or to sell anything from it for the benefit of his brother. Therefore, the mother's permission is not considered, because her disposal of his wealth must be for what is most beneficial for him [the minor].