On further reflection: I should have mentioned the value of finding the names of James' siblings or of all of his children. If you find them, you could use the Gaelic naming conventions to guide a search for James parents, because (if the naming conventions are followed) the names of the children predict the grandparents names. Same for Isobel. This is truly a long shot and should not be confused with proof, but might send further research off in a good direction.