Yes, you've got the right family. I do suspect that William who died on Manitoulin was Hannah's brother but having grown up in Bruce County and from my research into my grandmother's family, I know how many many McEwens there were at this time and so many with similar names that often nicknames were used to distinguish between the men of the same name.
If anyone could check the newspaper, The Expositor of Little Current, for an article about the accident that killed William and also an obituary, I would really appreciate it.This would be a real help and would help confirm my suspicions about William.