Interesting post, as my wife eventually found, through the internet, descendants of her G'Granduncle and G'Grandaunt who emigrated to Australia from Ireland. Two siblings went to the USA, two to Australia and one stayed put in Northern Ireland. Unfortunately, these were Harcourts and not Johnstons so they are irrelevant to Johnston-L. From the British Gov't birth records and census data, I am fairly convinced that the family of Robert Johnston and Christina Forsythe Johnston was composed of the two parents and four offspring, two boys and two girls, and all emigrated to America except for the patriarch himself. I presume that he died, which was possibly the catalyst the caused the family to pull up stakes and emigrate. One sister was apparently married in Scotland and emigrated with her husband.