IF your William IS the gunsmith from Nairne,,,,then he is NOT the William with Jemima on the 1861 census..
The William from Nairne father of Sarah DALTON was in Nairne in 1855 as per the marriage transcript..
26 April 1855 On the 21st instant, at St. Jame's Church, Blakiston, by the Rev. J. Fulford, Mr John BRAUNSTHAL, of Echunga, to Eleanor, eldest daughter of Mr. John DALTON, carpenter, of Nairne, and granddaughter of Mr. W. ALLINGHAM, gunsmith, of Nairne, formerly of Chatham, Kent.
I have many sites listing other Williams from Kent and some born same time,,but when I check them out they all die there or have different kids at the same dates as your Williams.
There was 2 other ALLINGHAM families that arrived together 1841 also with William and Elizabeth and Edward and Elizabeth as parents and with children Susan, Sarah, William, Anne, Charlotte, Jane, George, John, Mary, Christopher, Fanny...all from Ireland
Might be some of them are getting mixed up in the Aussie lines too