Hi Penny,
I agree with Frances that her surname on the IGI bapt entry could have been mistranscribed, and that you need to look at a copy of the parish register on LDS film. You can see these in Canada for a small fee through any of their Family History Centres (open to all). Look in the local phone book for "Church of Jesus Christ of Latter-Day Saints" Family History Centre or Genealogy, and they will give you their opening hours for non-members. They have a lot of free records on film, fiche, and online there as well, which will help you with your other questions.

The Lezayre parish register film is LDS no.0106727 [1696-1849].
You can find this number on the IGI entry for Charlotte at the bottom of the screen under "Source Call No.". You need to watch that you are using only "extracted" records on the IGI (extracted from the parish register).

You could order the Douglas and Braddan films for the other children's records as well, because they usually allow you to order several films at a time. They ring you when the film(s) arrive, and you book a film reader for a time which suits you. The films are usually yours for a month before they have to be returned. You can usually see bapts, marriages, and deaths on the same parish register film.
The Braddan film for their marriage (John Keanney/Margaret Fayle) on 4 July 1805 is LDS no.0106709 [1733-1817, marriages only].

The people transcribing the bapts/marriages for the IGI often made a stab at a surname and chose a familiar one. I was used to this after researching "Joughin". - You wouldn't believe the number of variations for this name in the IGI, almost all mistranscribed. I had to get all my details from the parish register films.

Sue