I finally broke down and added the information I found on John Robinson and his family to my genealogy program. I was hesitant about doing this because once you add information it becomes a pain (you know where) to remove it. Even though my instincts were telling me I had the right family, I'm still not sure. I think the hesitation comes from the fact that for John's place of birth all it says for each census record is 'England' which could me just about anywhere in the country. Much like for Edmund 'Canada' for his place of birth could also mean just about anywhere, although I've narrowed it down to Ontario simply because that's where his parents lived in all the Canadian census records I found them in.
The kicker for me anyway is the fact that John's wife is always referred to by initials M.E. except for one census where she's 'Eliza M.' I also solved the mystery of 'St.' George. Upon finding a death record for him in Silver City, Grant County, New Mexico it seems that the 'St.' is actually 'S.T.' initials, which makes more sense than his being a 'saint'. It also seems that each of the children including my great-great grandfather had at least 3 initials not counting their last name, which also fits what I already knew about him. According to Edmund's death certificate he's listed as 'Edmund Lowell C. Robinson'.
I found two more possibles for Mary (Eliza) Robinson's death in Canada, but again I'm not sure about them because the records don't give a whole lot of information. The last one I found is the most promising, May Robinson, died 26 Oct 1880 (which fits the timeline), born in England, married and the informant was John Robinson. Its entirely possible that the 'r' was left out of her name and that's why its listed as 'May' and not Mary, but who knows.
I also found a possible in the 1841 England census for Mary and her maiden name which has yet to be consistent since I've only seen it twice and spelled differently both times. So I'm going to do some digging on that particular family to see if I can gain any other clues about Mary.