Hi Southpaw58, the attachment worked fine.
I'll take each point in turn. Hopefully <<...>> will point to your reply.
<<Colonel Halkett’s regiment.>>
Was John Brash discharged when he married? If he served after 1760 his eventual discharge might be recorded in the National Archives at Kew under the WO 97 series.
<<There is also a death record 17/10/1798 for a Betty Brash Duntarvie.>>
I believe this to be recording the death of my 4xgtgdmother Betty Brash wife of Thomas Shatton. He is first recorded in Duntarvie on 18-12-1787 then through to his death 7-2-1816, and their daughter's death (Betty Chattie, born Betty Shatton in 1774) is recorded there on 27-7-1798, both deaths warranting a mortcloth at six shillings.
<<There is also an Elizabeth born around 1803 Abercorn who marries James Marshall 29/5/1827>>
This is Bathia Brash, I am sure.
This is the transcription I was given: "19-3-1895 12.20pm Elizabeth Brash Marshall age 92 [correct if Bathia], widow of James Marshall farm-labourer, at Philpstoon Abercorn, of John Brash quarryman & Elizabeth Brash ms Brown (both deceased). Cause: bronchitis 5d. Inf: James Marshall gson 508 Keppochhill Rd Glasgow [signed]." - D-1895-661(Abercorn)-5. I took a photo of their MI in Abercorn churchyard. It reads "Erected in 1886 / by / Robert Marshall / N.Z. / bro.William d. 12-7-1854 age 17 / father James Marshall 7-4-1879 age 82 / mother Elizabeth Brash 19-3-1895 age 92".
Did you know that Mary Brash d/o John Brash & Christina Clark had a paternity battle in 1843with a Hugh Fleming before marrying her cousin John Marshall s/o Elisabeth Brash & James Marshall?
<<maybe a seventh child Jane/Jean on 2/9/1804 in Abercorn (although this BC shows the parents as John Brash and Isobel Brown.>>
Rather than Betty being one of the seven, there is this Archibald I mentioned who died in 1797. This seems to confirm he was her child, because in this way Mary Wallace had four children and Betty Brown had three, making up the seven. Isobel and Elizabeth are frequently reckoned to be synonymous, so I think this justifies the mother being Betty Brown. There isn't any birth record for Archibald but that might be because all the other children's births weren't recorded until after Mary Wallace's death and possibly somewhat later - they are in a Register of Copy Certificates in the OPR so out of their natural placement.
Addition: I found Jane Brash's death registration (15/11/1870). Her mother is Betsey Brown and her father was unequivocally a dairyman. That settles it namewise. Occupationally odd though, although a dairyman can be a farmer looking after cows (needless to say....).
<<The Death record of Agnes ... says her father John was a quarryman....>>
Not surprisingly, my information on these family groups is incomplete, so it's new news to me that John Brash is recorded as a quarryman. Given that 'dairyman' was recorded first in time, could that have been subsequently misunderstood by later informants as 'quarryman'? No, I don't so either, but he was definitely a farmer in 1841. Also, I found a home for that 5 year old William Leitch: Janet Brash was either married to or had children by a Leitch - she was visiting her son John Leitch in 1861.
<<There is a grave in Abercorn erected.....>>
Yes, it's the best indicator of his parentage, and must mean he was around in 1841 which record at Milton Dalmey tallies - apart from him being a farmer - however there's no reason a retired quarryman wouldn't turn his hand at a spot of cultivation or dairying and call himself a farmer.
<<In relation to John B and Agnes Thomson, I have not found more information on this family to date, over and above the marriage and birth information. I have seen the reference to John Brash a farmer in Newton and you could be right. If any of their three children lived beyond 1855 (unlikely?) or left a detailed grave record might provide more data points?>>
I cannot find anything.
<<Could the John Brash (h/o Agnes Thomson) be the son of John B and Christian Greenlaw?>>
Could be thus marr 17-8-1758 Abercorn to Agnes Thomson, or equally thus marr 16-6-1758 Abercorn to Jannet Cummin. There's nothing I have found to say one way or another.
That's all!
You're most certainly not wasting my time. Far from it. I'm not entirely happy with my placement of Betty Brash w/o Thomas Shatton within the Brash dynasty, and resolving the placement of John Brash & Mary Wallace is likely to help.