My 6x great-grandmother was Janet Wilson married to Andrew Gammie (b.1711). Actually if you have been touch with both Alan and Stewart, then there is no need for me to give you all the info again. Mine came directly from Alan, who is my 4C1R. I have not verified/re-checked Alan's work as I am quite confident he has done a thorough job of it. My main line is Reidford, of which Alan is apparently doing a one-name study. On thing perhaps would be to double check which John Gammie Elspet Elder married, on 30 June 1776, Marnoch. She was born in 1752, Fordyce, daughter of John Elder and Janet Cowie.
Is it perhaps possible that Alan did confuse the two Johns? I wouldn't have thought so. They also could have been cousins, but raised as brothers, hence the same names and being heir to the same *father*. I do not have any sblings for our John and one brother George, for his father Andrew. I would have expected your Alexander to have a sibling named George. Also, you have Gamy for all the siblings, so Gammie doesn't really *fit* with them. Most likely they are related (assuming they are in the same village/general location), but somehow the names were spelled differently. I have seen Gamie and Camie/Cammie used by others.
Are you by chance connected to any Reidfords, other than Elizabeth Gammie or other surnames closely connected to them in descending generations? I see some names turn up several times, Harper, Morrison, Pirie for example, down along the lines. Am sure many of them were marrying cousins or cousins of cousins.
If I can be of any help let me know, though I am not sure how I can.
Cheers ... Toni