Once again, great detective work Joe. Yes, Elizabeth certainly is the daughter of Robert Fell and Eleanor Gibson.
I would like Mary's household detals from the 1871 Census thankyou.
I don't think that the Joseph Horatio you found is the right one. I have his birth on the IGI as 1799 and his name was Horatio Pitt Gibson, believed to be the illegitimate son of William Pitt the younger and Mary Gibson Will never be able to prove that of course as he was born some months after Pitt died. Funny thing though, the Australian family had never heard of Horatio but Granny insisted her Granny was the grandaughter of William Pitt the Younger, through the Gibson family so that's why I went looking and was amazed to find Horatio Pit Gibson. All the books say Pitt died childless. My guess is he mightn't have even known Mary was pregnant!
With this info we could rewrite the history books

Many thnaks again, Marie