I hope that I'm not guilty of putting two and two together and making five !

The Edward Forbes who married Isabella Looney (daughter of William Looney, farmer) in London in 1845, described himself as a widower gentleman, son of Edward Forbes, merchant. This matches the only Edward Forbes who was listed in the 1841 IOM census ie Edward Forbes b 1786, banker (and father of Edward Forbes b 1815, naturalist), who, by 1842, was seeing his comfortable existence coming to an end with the collapse of his bank.

The christening record of Charles Theodore Forbes b 1841 (Douglas IOM) shows that his parents were Edward Forbes and Isabella Looney, and the record of Alfred Theodore Forbes b Dec 1842 (bap Grindon, Staffordshire Jan 1843) shows that his parents were Edward Forbes and Isabel (no mother's surname given)

I haven't discovered what happened to Edward b 1786 or Isabella nee Looney (b 1814 ?) after their 1845 marriage, nor what became of their 2 sons in the years before they emigrated to Australia. Perhaps the whole family emigrated together in the late 1840s ?