Hi John.
Glad it was a help.
http://newspapers.nla.gov.au/ndp/del/search?adv=yHere I have noted the Funeral Notices, 3 of them, placed in the Sydney Morning Herald on 3/8/1918 relating to
WILLIAM RUFUS WALLIS1. Mrs GRACE WALLIS of 48 Westbourne St. Petersham invites......friends... her dear husband
2.Friends of...Mrs T ALLEN ( this is dau. CASSY DIANA), Mrs H. KNIGHT ( this is dau.ELLEN) Mrs J. CUDDIHY ( this is dau. LAURA) Mr LOU. WALLIS (this is son LOUIS) and Mr BERT WALLIS (ALBERT perhaps) invite them ..... our dear father.
{The marriages for these people can be found on the Qld and NSW indexes, the links for which you have.}
3. Friends of Mr JOHN WALLIS and
MR and MRS C EDWARDS invite them ......their dear
BROTHER.
So it seems there was another WALLIS sibling in Australia (female)
As has been posted,GEORGE HENRY WALLIS died in 1918 too.
There was a Legal Notice in the Sydney Morning Herald of 8th August 1918. It tells us he was a ganger of Petersham.
Interestingly the Sands Directory of 1895 shows GEORGE WALLIS at 20 Windsor Rd. Petersham
and
JOHN WALLIS at 18 Windsor Rd Petersham.
Perhaps it is them

Sue