Sue,
I was just about to post a message with the same conclusion. Caesar and his Fynney family are well documented outside of the census, I have him in South Africa in 1850 and Australia in 1855 (perhaps I should check the birth records there for Dixon!). He is also mentioned in a History of Leek (his birth place) published during his lifetime, which shows him as a hunter (prey not specified) and that he had interests in IOM.
Thank you for your detailed and helpful messages. I was thinking about obtaining Maude Louise's birth certificate from the IOM registry, will it have her mothers maiden name on it as with the English certificates, also what would I be likely to see on the death certificates for the other siblings?
Another interesting point is that the names Augustus, Georgius and Maude Louise feature a good deal in the Fynney line!
I intend to obtain Caesar's will, I shall have to consult Ancestry as I only have FMP at present. In a Fynney will that I have there is reference to an "Indenture of Settlement in favour of Mrs. Susan Fynney" whereby funds are given to the trustees of the settlement. What that means I do not know. Does she get some cash for keeping quiet about Mr. Dixon!?
As a point of interest Caesar married a Jane Morris in 1841 she dies in Hayfield in 1878 but as you point out the woman Susan Jones is with him as a visitor in 1881 I have not been able to see any other marriage for Caesar, it seems like Susan became Mrs. after his death and that fact is accepted by the family as evidenced by the will I refer to and the Indenture of Settlement which was set up by Caesar's very wealthy brother in 1888.
Thank you again, it is very helpful to go over these matters with other researchers. I start to wonder at times is it wishful thinking rather than evidence based.

Martin