Jas A Collett born c1890 sailed to Fremantle in 1914.
http://www.bdm.dotag.wa.gov.au/_apps/pioneersindex/default.aspxJames A Collett married Frances M Ebbett in Blackwood, Western Australia, in 1916.
The index shows no births to that marriage, to 1931.
James Arthur Collett, aged 72, son of Edward C and Ann C, died in Blackwood in 1962.
Francis (sic) Mary Collett, aged 70, daughter of Thomas F and Grace, died in Blackwood in 1959.
There are no Collett deaths to 1961 showing father's name James.
So it seems likely the couple didn't have children, as they were married and died in the same location.
Frances Ebbett was born 1889 in Helston reg dist.
Thomas Ebbett and Grace Matthews were married 1880 in Falmouth reg dist.
Grace probably died in 1899 in St Germans, aged 40.
Thomas F died in 1949 in Penzance, aged 91.
Thomas remarried in 1901 to Sarah Collings Clemow. She died in 1922, and it looks like he then immediately married a relation! -- Ellen Clemow.
In 1901, Thomas and wife Sarah C in St Keverne, Cornwall, are with children:
Frances Mary
Thomas Hope 1892
Henry Alfred Vincent 1894
Thomas and Sarah apparently did not have children of their own.
I'm not seeing a record of Frances Ebbett's passage to Australia.
You might be able to find descendants of Frances's brothers who had kept in touch with her in Australia.