Thanks for the info Brian, I've managed to find info on the Dumpheys, it's the Callows I'm struggling with.

John William is found on board the "Prince William" in Liverpool docks in the 1901 census and it is from his age given there and from his wedding certificate that we have an approx year of 1875 for his birth. Checking the census returns prior to that I can't seem to tally him with another John (or John William) Callow. Equally I can't currently narrow the choices of his father since I lack enough info. I have searched the BMD records on my last visit to the Island but cannot find a likely birth entry for JWC (ie none with a father called William in Braddan or Douglas.)

I think it unlikely Sgt Callow is the same William Callow I'm looking for but it would be nice to eliminate him if nothing else. According to the Will transcript on your site Sgt Callow had a son called John which I know is a long shot but at least it's something to look at!