The Scots can use either their sept name or clan name. My gg grandfather John McGillawee signing legal documents one year he would be McGillawee and the next year he would signs the documents as Lamond. It has been driving the family researchers nuts. I have in my possession photocopies of letters one John McGillawee/Lamond sent to his brother in Scotland Robert Lammond. Another is a letter
from Robert's girls address to their Uncle John.
With your second question again it is to do with the sept and clan name. On the marriage cetificate she used her clan name but in Canada she used her sept name.
Hope to hear from you as you might have another piece of the puzzle that would help us over here.