My family also orginated in Kelso. My great-great grandfather was James Fairbairn, b. 1786; married Helen Goodfellow in 1812. They emigrated to Spencerville in Canada in about 1844 with their eight kids. I have detailed records of all James' descendants, but nothing on his ancestors. There is some indication he is related to Sir William, but the tie is not clear.
If anyone has James/Helen Goodfellow in their tree, it would be great to hear.