Can you also give reference as to where/how the names of other's supplied came to be please?
Other names were
John Angus,
James Andrew,
And possibly Donald
Were they siblings of Isabella & was there no date & place of parents marriage on any of them?
Isabella, (1st born) 1855 with mother's birth year c 1821 so mother would have been 34, not impossible but questionable whether she may have been married previously?
What years were the others baptised & are they in order of birth on your list as this may help to identify parents with scottish naming pattern?
When did it become "law" for birth registration in Canada ?
Did Isabella marry, if so, did her marriage give her mother's maiden name or does it give a "previously" name too, if she was indeed married a 2nd time?
Have you looked for the family 1861/71/91/1901 & when did Sarah die?
Where were the family living in 1881 as the deaths/burials may be recorded in the same area?
Annie