in real life the second captain was James Thomson, who was taken captive with the rest

Wasn't the second one Captain Sweetenham? I'm at my parents' place now, but I can check tomorrow. Anyway, IIRC, Keith's fate is a sort of amalgam of the two captains': Scott was taken to Achnacarry and his wounds dressed, etc, like Keith at Ardroy, but Sweetenham was taken along to Glenfinnan like Keith.

Oh, interesting about the actual Windhams, I hadn't dug so deep on them!

Here's the Well of the Seven Heads.