Hi carole,
May possibly have found an 1841 Census return for the whole family, though the writing isn't too great as it looks as if its been rewritten over afterwards......probably faded with time.
Its 1841 Hartcliffe & Bedminster Somerset
Wiiliam Wyatt 30 Mason
Mary 30
John 7
Ester 5
Mary 3
Ellen 8 mths ( did wonder if this might be William, (Wllm) and poor writing has made it look like
Ellen or perhaps its just wishful thinking)
It has stated 'Not' born in that County for them, this may tie in with the death you found in Bath, and why William 1840, sometimes has Bath as birthplace.
Maybe the mother comes from Somerset , could this be why William and Mary's marriage isn't in Cornwall records?

Do you think???
Sorry I keep bothering you with this, but they just seem to disappear between 1841 (if thats them) and getting married in London in the mid 1850's.
Also wanted to ask if William 1810 and his brother and his Dad, John, were all Masons, would this mean that they belonged to the Masons?

?
Only I was reading on one of the links that St.Austell had quite a strong Masonic tie and wondered if perhaps that might be a line of enquiry???
Again many Thanks eita