That's great! Your g-g grandfather George was a brother to my g-g grandmother Margaret!
I believe (altho cannot confirm) that Flora McNair may have been born around 1816 as the census record from 1841 has her age as 25 (and John Jackson was 35). Margaret was 3 and George was 1. And be darn'ed if I know the area of the census! The page that I printed off doesn't have the area and the only thing I see is chicken scratch so can't read it!
I am wondering if they came from the Isle of Gigha, as Margaret and her husband (Peter McCallum) lived there at some point.
Just trying to get information on Flora McNair Jackson!!! But it's so tough! I am planning a trip to Scotland in August and hope to do some investigating!