These have got to be two different couples - even if they had the same surname the ones married in 1909 obviously cannot be the parents of a son born in 1879.
The first couple in the thread, from 7 years ago, is William Donald and his wife Elizabeth Ann Scott, married in 1909.
Yours are the family of Duncan Scott and Mary McDonell, who were married in Inverness in 1861.
As their daughter Elizabeth was born in 1865, she is obviously not the one who married William Donald in 1909. Even if Joyce had not said that her Elizabeth Ann Scott was born in 1887 in Buckie, it is hardly likely that your Elizabeth Scott would have started a family after marrying at the age of 44.
You can get a digital image of the 1861 marriage certificate at modest cost from
www.scotlandspeople.gov.uk Have youhad a look in
http://libindx.moray.gov.uk/mainmenu.asp?