To get others to show interest, what info do you have on the family. A quick check of the IGI shows William and Harriet marrying on 22 Dec 138 , St Nicholas, Aberdeen. An extracted record.
A search from 1820 to 1860 shows only one child born to them in either Scotland or England - Christina McKay Gunn. - on 08 Nov 1839. I'm sure you must already have this info.
A search for Australia for the same couple in the same timeframe finds no births.
No sign of them on the 1841 census.
As your'e probably aware - if either had died in Scotland after 1855 - their parents names would have been on their death entries.
Regards, Steve :O)
Logged
McDonald originating in Aberlour. Smith (Aberdeenshire/Aberdeen), Esslemont, Christie, Robbie; Scott (in Aberdour). Crosbie and Willison. Roxburgh: Lawrie, Thomson, Paxton, Peacock, Amos, Robson