I don’t think he is the son of Laird of Craig Thomas Johnston.
Thomas of Craig had a son named James who was living in Scotland in 1716.
James Johnston, litster in Aberdeen
So this profile needs more research and documents. I’m disconnecting from parents.
To be more detailed.
===Disputed Origins
Seen as the son of Laird of Craig Thomas Johnston & Mary Irvine which would make him the same person as James Johnston, litster in Aberdeen - who was noted as husband of Jean Ogilvy in Aberdeen in 1716. Not quite making sense, so if you can explain - discuss.