I am related to James Boyack who was David's brother.James Boyack who was married to Ann Renny had 6 children,William,James, David,Richard,Alfred and George.Their son James married Margaret Powrie.They had 9 children,Jane Annie,Helen,Henrietta,Jane Anne(Jean),Margaret,Elizabeth,James,Edith(my Nana)and Andrew.
I believe that the James Boyack who married Ann Stevenson died in 1858 and his parents were David Boyack,a tailor and Ann Shaw in Dundee.The origins of the Boyacks could be The Freesian Islands or Germany but only heresay i'm afraid.