Hi Kimmy & welcome to Rootschat

This is the marriage of James & Harriet from the Sussex Marriage Index;
Birdham, West Sussex, 3 Nov 1834:
James LELLIOTT
Harriet MAY
It seems that James died December Q 1842, Westhampnett registration District (7 353) This from FreeBMD.
It also appears that Samuel Hockin married the widowed Harriet, September Q 1850, Westhampnett (7 755)
In 1861 - West Wittering Ssx RG9/617/33/1
Samuel G. Hockin 44 Shoeman b. Cornwall
Harriett 49 b. Birdham
Richard 14 ditto
Ann 10 b. Itchenor Ssx
Mary A 6 b. West Wittering.
No sign of William on the 1861 census so you might start looking for his emmigration to Oz between 1851-1861. There is a page here on Rootschat dealing with emigration to Oz, perhaps you can try some of the links posted there or ask for help if you get stuck.
http://www.rootschat.com/forum/index.php/board,165.0.htmlDid spot his brother, James who was married in 1861 & living in Sussex.
Harriott seems to have died June Q 1864, Westhampnett reg. district (2b 197) & Samuel, Dec. 1871 aged 54, Westhampnett (2b 207)
Hope this has been of some help,
jane