Hi browny000,
Williamina didn't marry John BROWN. She married Joseph Henry LAMB in 1903 and the bigamy charge was because she married Edward HANSEN in 1925 while LAMB was still living. This is unfortunate because John's parents would have been named on a marriage cert.
There are a few items on TROVE about the arrival of the 'Hermes' in 1906. It was a cargo ship, not an immigrant ship so he may have been crew. You would need to check with Queensland Archives to see if a crew/passenger list has survived.
Queensland registered the deaths of those who fell in WW1, and the reg. numbers are prefixed by an "F". This is your John:
Death Registered 1922
Died 9 Oct 1917
Reg. Number: F1040
John BROWN aged 30
Unfortunately no parents' names are given, and I doubt that his name was John BROWN - BRUN perhaps?
The Mt Morgan burials are on the Rockhampton Council's website (as a PDF). Alfred was born in Mackay.
Debra