http://www.bdm.nsw.gov.au/familyHistory/search.htmTess, you can search for the Australian part of this family here. Frederick William Dumont and wife Florrie/Florence appear to have had children Clarice M, James, Albert H and Walter J, younger siblings to the Frederick William who died in WWI. James died 1901. Clarice M died 1905. That leaves Albert H and Walter J's descendants if you want to find descendents of this line.
Marriages: Albert H. Dumont m. Audrey Lean, 1924.
Walter J. Dumont m. Milicent A. A. Flack, 1928
(also if you're going back, the marriage of Frederick William Dumont and FLorence Morris is also listed)
Deaths:
Frederick William Dumont son of Abraham and Margaret d. 1938
Florence Dumont, father William, d. 1950
There's also a James Dumont d. 1951, parents also Abraham and Margaret.