The Knights of St Lazarus were a militant and hospitalier ( belonging to certain religious orders who treat patients in hospitals )order in the Middle ages. Their primary focus was care and treatment of lepers. They were not composed of lepers however.
When Princess Isabella and Princess Margaret are out hawking, they are depicted riding sidesaddle. In fact, the earliest functional sidesaddle was credited to Anne of Bohemia, over 75 years after these events.