QLD State Archives provides an online Passenger lists for emigration in the 1800s, Series ID 13086 is the reference.

Thomas Wilson emigrated to Australia first in 1885, aged 19 years on the Ship Dacca, London to Townsville.   He travelled as indentured, meaning a future Australian employer paid his passage, in return for a few years work.

Catherine Wilson, Abraham & Robert,  emigrated to Australia on SS Roma.  The ship sailed from London on the 30 October 1891, arriving  Brisbane 22 December 1891.  Abraham was listed as 12 years old, but he was actually 15 years old.  This might have been to pay a lower fare (as a child).  Abraham, travelling in steerage, disembarked in Rockhampton, 18 December 1891 (SS Roma arrival date confirmed in Rockhampton Newspaper Morning Bulletin).  Catherine’s age was listed as 40, occupation ‘wife’.  She also travelled in steerage, however her disembarkation point was listed as Townsville.

On SS Roma, Catherine, Robert and  Abraham were listed separately, not as part of a family group, as is normally the case on then Ship passenger lists.  The Ship passenger lists in National Archives show names of passengers meticulously recorded in alphabetical (surname) order, with family groups listed under the name of the father.  Ages are also recorded, and whether the passenger is male, female, married, single, child or infant (less than 12 months).

Abraham’s name does not appear under a family grouping, so he initially appeared to have travelled alone.  It was only because he was so young that I eventually referred back to the passenger list to see if there were more Wilson family listed.