Hi Andy,
John Thomas was my great, great grandfather too!! He had another son Allan who married a Katie Holmes, they had a Robert Cojeen, who in turn married Essie Clarke who in turn had my mum Sylvia who then married my father Ken Cowell!
So this must make us cousins of some sort! I have been in contact with another of Williams brothers family. They are descended from Robert.
I have a photograph that I would be interested in sending you as I think it is John Thomas with his captains hat on.
Drop me an email at sanjones@wn.com.au
Cheers,
sadny