" There are witnesses tho - Louis Barriere in lieu of the father. His Godmother wasn't there."
Was Eusebe of legal age (would be 21 or older) at the time of his marriage? Louis Barriere is listed as a witness only, and not giving consent, correct?
Women were usually not included as witnesses in the marriage records, even if they were present at the event. You'll find that practice changed in more recent records.
What was Louis Barriere's relationship to the Fountain line, have you found any? Obviously, it was more than a passing relationship.
"She had four daughters that are possiblities: 1 16 year old, 1 14 year old and the other two I can't find birth records for."
Well, that might be a lead, one of the older daughters could possibly given birth out of wedlock.
The choice of a surname is interesting, I would venture it wasn't pulled out of thin air. A known dit for Soutiere is
You're doing a great job finding and putting puzzle pieces together, keep going......