A Candy family historian has told me that Henry and William (b.1808) both had the same father, but different mothers.
The mother of William, the older brother, was Hannah Billing(s) while Henry's mother was Mary Billing(s).
On Ancestry.com I found three baptisms of children born to a William and Hannah Mawbey in Surrey at around the right time:
John bap. 12 March 1797;
Elizabeth, bap. 16 January 1799;
Mary bap. 8 June 1804.
All three baptisms took place at St George the Martyr church, Surrey, England.
Maybe Hannah died after the birth of William in 1808, and her husband re-married her sister, Mary?
Was Henry, the son of William and Mary Mawbey (nee Billings), in Tasmania in the 1830s because his younger brother, Joseph (aka John) was there as a convict?
Was Henry in fact Joseph, having changed his name because he was an escaped convict?
Too far fetched.
Judging by Hobart newspaper reports of Joseph's two court appearances there, he was about 10 in January 1835, indicating he was born c.1825.
Henry married in Melbourne in November 1842.
If he was aged around 20 then, he was born c.1822.
The other Tasmanian Mawbey convict, John Mawbey, did not arrive until 1842.
A John Mawbey sailed from Launceston to Melbourne on the Yarra Yarra in 1852.
Which one was he?