Hello Allan
So I'm not alone out there!
I too have been researching the Cretney line and trying to put the pieces together, maybe between us we can compile a history? My link with James & Margaret is also via his son John and then with his son Thomas (1813) who married Ann Eliza Murray. His son - again a Thomas (1842) married Sarah Ellen Hammond/Woodyer and they left the island and settled in Salford, Manchester. His son, my grandfather, was Arthur Edmund Cretney (1886) and my father Arthur Ronald (1921) brings us to me. Unfortunately my brother, the last Cretney in our line, died in 1983 so I decided to take up the cudgels and find out about our roots.
If you want to keep in touch or swap information, we could do so via e-mail - let me know.
Thanks for the information regarding James & Margaret, now I can get on a bit further!