Hi ShaunJ,
Did you notice that Hugh jnr (died in 1980's) had been in Australia for years? Giving a migration date of ca 1950's. And his mother Mary (died 1960's) had been in Australia 10 years - giving a migration date of ca 1950's
It seems possible, then, that the 1933 trip (assuming it was this Mary) might have been a recuperative sea voyage following the 1932 death of Hugh THORNTON/Euclid Hope BUTTERWORTH. And that Mary, son Hugh, his wife Bessie, and their children might have migrated together in 1950's
JAP
PS: I wonder where PRF submitter Gerald E BARNARD fits in to the picture (incidentally, the telephone directory at:
http://www.whitepages.com.au/wp/initResSearch.dolists only an H BARNARD at the address given for the submitter).
PPS (added later): The PRF says that Bessie, wife of Hugh Spence Abbey THORNTON, died 1990's Queensland