My primary interest is in Mary McMillan McCormick, as she was my great grandmother, having had my grandfather Archibald McMillan Watson out of wedlock in Glasgow in 1901 (given his father's surname). I am trying to find out when and how she came to be in Kingston/Amherst Island. She left Archie to be raised by her parents in Glasgow, and he never knew much of his mother's life in Ontario, even though he emigrated to Western Canada at 21 years of age.
From the marriage certificate of Robert McCormick and Mary McMillan in Kingston in 1906, I found Robert's parents listed as William McCormick and Eliza Beggs. They can be found on IGI search as married in 08 NOV 1867 Glastry, Down, Ireland. IGI will also give names of first three children (daughters) born in Ireland, before they moved to Scotland, so there is your Irish/Scottish background.
Here is the family of Robert McCormick on 1881 UK Census:
Dwelling: Machribeg Cottage
Census Place: Southend, Argyll, Scotland
William MACCORMICK M 35 M Down, Ireland
Eliza MACCORMICK M 30 F Down, Ireland
Sarah MACCORMICK U 12 F Down, Ireland
Mary Jane MACCORMICK 7 F Down, Ireland
Robert MACCORMICK 4 M Galloway Wigton
William MACCORMICK 1 M Southend, Argyll, Scotland
Looks like your Hugh, if he was Robert's brother, was born after 1881 census. What year were Hugh & Edith married and do you know when Hugh came to Canada? A witness at the marriage of Robert & Mary was an Alex McCormick. Not sure if this might be another younger brother or one of the cousins from Amherst Island.
The other McCormack's on Amherst Island seem to have been there for quite some time, heads of familes having been born in Ireland, some were Presbyterian, some were Catholic familes and can be found on 1881 Canadian census on LDS site www.familysearch.org
. I assume but have not yet searched for relationship of Robert's father William to the other Amherst McCormack's from Ireland. It would seem likely that William was a brother to them, and that Robert came from Scotland to Amherst Island because he had uncles and cousins there.