Julius Higgins was the name adopted by Julius Karoly, a Jew named from Szombathelny in Hungary who settled in Ireland. His brother John and sister Agatha subsequently followed him to Europe, and started new lives in England. Their father is simply known to scholars as Mr. Karoly.
The extended Karoly family is discussed in Tarzan Alive. Wold Newton researcher Mark Brown further established that Julius Higgins was also the father of two brothers named Octavius and Claudius, respectively the father of Henry Higgins and grandfather of Rick Blaine.