I'm adding another reference to this discussion
From http://www.clanmacfarlanegenealogy.info/genealogy/TNGWebsite/getper...
Notes
The identity of Thomas Erskine's wife is not certain. She may not have been a daughter of the 1st Earl of Morton although that is often stated, sometimes as Elizabeth but perhaps more often as Janet.
Cites
Sources
[S474] Colquoun_Cunningham.ged, Jamie Vans.
[S105] Andrew Cuninghame, 1st Laird of Drumquhassil, Blaine L. Berkowitz, Esq, MBE (Hon), FRSA, FZS, Kt.C. OEG, (recieved as e-mail attachment 10 Feb 2012).
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Stir net (membership required) has the line
http://www.stirnet.com/genie/data/british/dd/douglas03.php#link3
(c) Janet Douglas (d before 21.02.1490-1) --
m. Patrick Hepburn, 1st Earl of Bothwell (d 18.10.1508) --
(d) Elizabeth or Janet Douglas --
The identity of Thomas Erskine's wife is not certain. She may not have been a daughter of the 1st Earl of Morton although that is often stated, sometimes as Elizabeth but perhaps more often as Janet.
m. Thomas Erskine, 2nd Lord (d by 1493) --
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Macfarlane Clan (above) has this Elizabeth / Janet marrying 2nd to the 5th of Craigdarroch.
I also saw this Elizabeth in a tree as daughter? of Archibald "bell the cat" Douglas, which would make more sense to me, as there might have been a Glencairn property connection?
I'm taking care of the under documented daughter of Joan of Scotland merge warnings.