Organ donation, what if the next of kin the spouse is dead , and the siblings are a minor can they still decide to donate the organ?

Yes, they can donate: Most states now use the driver's license to obtain consent. If the person has declared their wish to donate previously, this is sufficient consent. Also, in the case where only minor survivors existed and no previous declaration of consent had been documented, the organ procurement organization would probably accept the consent of the minor relative.