Hi,
This is what I have on James Martin and Margaret Jaffrey. I believe it is correct but if you find any errors, please let me know.
James Martin - born March 1750, Belhelvie ( I have 8th March as the date but not sure whether that is birth or baptism). He was the son of James Martin and Margaret Seymour ( married 4th November 1740, New Machar), who also had offspring Margaret, John, Joseph and Jean.
Margaret Jaffrey ( Or Jaffray) 8th Oct 1751, Belhelvie. Parents were William Jaffrey and Jean Laurenson, married 16th June 1747, Logie Buchan. They had other offspring - Jean, Agnes, William, Agnes, John and Robert.
Jean Laurenson ( spellings vary), 5th May, 1717, was the daughter of George Laurenson and Janet Murdo, married 26th June 1716, Logie Buchan. They also had Janet and Agnes.
That's as much as I can tell you about these people. I did have the James Martin/ Christian Harvey information and I have their offspring as Margaret, James, Mary and Christian. Does that match with what you have?
Regards,
Jen