Your father is quite right. The Johnston/es were quite a famous border clan. They were situated at Ayr. The borders were famously lawless, and the Johnstons were known as the "gentle Johnstons" which was used ironically. They were anything but gentle, but eventually the border clans were disarmed and brought under control by the English. My Johnstons left Scotland between 1704 and 1708 and came to Pennsylvania.