I know the topic was posted 7 years ago, but I've just stumbled across it.
As far as James Gloag Aitchison (child of James Aitchison and Robina Campbell) goes, I may be able to provide some information, his siblings, however, I'm not sure.
James Gloag Aitchison married a Susan Armstrong (also from Scotland) though I am unsure whether it was prior to migration to Adelaide, Australia. I am aware of them having one son, though there may well be more, it's what I'm searching for.
Frederick Francis Aitchison was born in 1886, and died 1964, after marrying Jessica Harrison (1898 - 1977) with whom he had children with, Doreen (still living, eldest), Frederick, Phillip, and James Sydney Aitchison (youngest, born 11 March 1932, still living). He was a Mariner, and served Australia in both the first and second world wars. His wife, Jessica, was born in Riverstone, NSW and was the daughter of William Oldfield Harrison and Annie Crouch, both of Scots ancestry.
James Sydney Aitchison married Pamela Faye Hughes (died 2007) in 1955 (roughly), together they had Edward, David, Fiona and Andrew, all of whom are still living.