It looks like John 1826 married twice, first to Catherine Clucas in 1850 and then to Judith (Julia) Lace in 1857. However there is also an entry for a George b. 1847 s/o John Greggor and Isabella Archibald so perhaps John was married 3 times although I can't find this marriage.
John, Judith/ Julia and George 1847 and their offspring can all be found in 1871/1881 censuses and the IGI but e-mail me if you would like details (see my user profile).

Jane