On the Qld death indexes, found the following :- 1.de Vaux - Walter Ranson d 3 Dec 1933 ref B 022757 , f. Cuthbert and m. as Annie Desmond.
2.de Vaux - Rose Maria d 9 Sep 1941 ref B 053699, f. Thomas Kiff and m. as Mary Jones Checked the de Vaux births to 1918 and didn't find any others born to this couple.
On the WW1 and WW2 Australian army lists was a Walter Ransome De Vaux, b 22 Jan 1889 at London, Canada. He married Florence Plant in England during WW1. They both ended up in Victoria, Australia and Walter d 1954 aged 70, parents u/k, Florence d 1947 with parents listed as David Plant and Phoebe Elizabeth Miles. Don't know if this is any connection but it was odd, they both have the same/similiar names.
If you obtain the death certificate for Rose, it should list all of their children. An alternative would be to check the funeral notices in the Brisbane Courier-Mail. Most major city libraries hold old newspapers on films.