AMMAN, Jordan—A Jordanian state security court on Monday sentenced two former officials to serve 15 years in prison over an alleged plot against the Western-allied monarchy involving the half-brother of King Abdullah II. Bassem Awadallah, who has U.S. citizenship and once served as a top aide to King Abdullah II, and Sharif Hassan bin Zaid, a member of the royal family, were found guilty of sedition and incitement charges. They are alleged to have conspired with Prince Hamzah, the king’s half-brother, and to have sought foreign assistance. Awadallah’s U.S.-based lawyer slammed the verdict, saying there had been a “complete lack of due process” and that his client had suffered “inhumane treatment, including beatings and psychological torture.” Lawyers for both defendants said they would appeal the verdict. They two men were swept up in a wave of arrests in April and Hamzah was placed under house arrest. Hamzah denied the allegations …