Thomas, your family member was Thomas, and not George. Sorry about that.
Isabella McGlasson, wife of Robert Stewart McNab, is the difficult one to research, as there are missing records, and maybe two women with same name. It's possible that her father was Peter McGlasson and her mother Jean McCrostie who was born or baptised Moulin 15th July 1760. If so, Jean's father was Patrick McCrostie born/baptised 18th May 1746, Monzievairdie & Stowan, and her mother Jean Fleeming, born Moulin 1748.
You may already know this, of course.