The LDS web site has a record of a Lucy 'Langille' (i.e. her married name) AFN: 1K0V-HPP, married to your William. He was the son of John David not John George, who was David Langille's son.
BTW, do you have any more info on Lucy? I know she was interred in Maine but I can't find anything else on her. The LDS site show's her as incorrectly being the daughter of her father-in-law! an serious error indeed.