This document will show you what information is recorded on a death certificate, Western Australia.
http://www.jaunay.com/bdm.htmlThe informant for the death certificate, 1916, does not give a name for mother of Hugh John GRIFFITH, and sister Hannah is deceased.
"Family stories had him leaving Caernarfonshire and going to South Africa,"
Is this a family story that resulted from an earlier researcher looking around for Hugh GRIFFITH?...does this support the family story, or is it how the family story began?
Your heading has him as Hugh GRIFFITH. Do you see your Hugh, sister of Hannah, with a second given name?