So, here is my assessment of the situation regarding Smythe's early life, and my best guesstimation;
Eliza Bridge from Hoxton did indeed marry an Edward Smith, a likely bookseller of Paternoster Row or commercial traveller (jobs changed very quickly in that wage bracket) and that this Edward was in fact the son of the victualler George Smith, turned shawl seller of the famous Indiana Shawl Warehouse, which lasted for a while then George once again went back to la vie de vitaille. It was during this period that his son Edward was very likely a traveller, as George had been. Then in my scenario, Edward ups and dies, splits his tome asunder, rips the binding and is a signature in the book of life no longer. Then his widow takes a lover, a man from the Sparrow family, who fosters the rest of the brood, Robert, Elizabeth, George and Frederic. Edward her first son being very likely the actual 'Smith'.
The Sparrows were intimately connected with Ludgate Hill, through two of shoot premises, belonging to Frederick, Robert and Henry Sparrow. In addition there was a wine connection with the sister of these gentleman who had married a welsh wine merchant Thomas Phythian which gave rise to more dynastical tea tentacles as well as a department store. There is a Henry Sparrow who dies early to fit the bill of progenitor zero and and Owen Sparrow, suspect of character but described as commercial traveller.
Two other relations, Henry and George went into coffee and made a laudable eponymic tilt of the shop shingle.
So there its is, Robert Smith, emigrant to Australia to escape the soot and mire of London came to Australia and became Robert Sparrow Smythe, a dedication to he real father and his patrinominal father - and his first family he visited when he arrived in 1855 was his brother, his eldest brother (step-brother perhaps) Edward, a man who had tired working and owning a vineyard in Clare, south Australia, starting a school there and eventually marrying three times, the last to his first cousin Jane Bridge, who if I have my imaginings right, was his half-first cousin.
Its even more complicated than this but I don't want to compete with the shuttle jockeys at Gaquelin in levels of complexity and dazzling speed.
At the moment there is a faint lead, the great, great grandson of Elizabeth Smith (married Edward Steele) name David Anthony Steele, currently my age and director of the family trust that deals in the leasing of the magnificent family Hall in Suffollk. I have sent a letter and emails to all those whose help can be mustered. Let us see.
If nothing else, I have all they need to know on the Steeles if they have it not already.