Thanks for the added details. I don't have the answer for the moment, but I will come back to you when I find something.
Now it is likely that John and Violet had more children. Of course thay may have died young. For John himself, I understand that he died in Manitoba, am I correct ? If so, he may have been buried under the French name Jean, instead of John.
Also, I have dozens of Joseph Ducharme in my files. By any chance, do you have his wife's name ?