Thanks for replying.
John Corjeag/Cavendish was the eldest of 4 children mentioned in the will of Thomas Cavendish (married Margaret Killey). Thomas jnr & Richard had significant bequests, but Jane (who, I think went to Australia at some time - would love to find out about her too!) and John just had token legacies presumably because they had emigrated many years before. A descendant of his called Smith visited my parents home in the IOM in the early 1970s, but any information they brought never came my way unfortunately, and I would like to try and fill in the huge gap between John's leaving the IOM, presumably before 1841 - can't see him on the census - and the arrival of the Smiths!
Any 'jigsaw pieces' you would like to share would be very welcome.