I found your name on the McDermott Genealogy Forum. Your email address seem to be the wrong one. Please contact me at firstname.lastname@example.org concerning the McDermott family.
When John McDermott married Ursula Lavallee on August 4,1835 in Saint-Athanase d’Iberville, the register shows he was widow of Francoise Elison ( someone wrote Ebsen or Ebson ). Do you found this fact during your research ? On that day off August 4,1835, the priest wrote his name : John McDonald... When his daughter Julie get married, her name change to McDorman...
Do you want to see this register document ?
Somewhere else, I do read he was Irishman. In your message on the Forum, you said he was British.