Kate
I don't know if you ever had a reply to this. Sorry I can't help either, but was interested in your ancestors. Actually I was looking for Merrylees at the time of finding this - but anyhow...
One of the ancestors is William Horsburgh (Horseurgh) who married Margaret Skirving in 1756 (Prestonkirk). When tracing their descendents her name is variously given as Skirving/Skirven. They lived and died in Morham, East Lothian, Scotland.
Is she a part of your history?
DaveW