You need to account for all children born to James ALLEN and Elizabeth in case your John Edwin travelled to NSW with a sibling. A death certificate, NSW, 1889, will record children, with, hopefully, names and ages. When James dies, 1889, his children are around which would encourage you to hope that they record useful information on father's death certificate.
This death certificate would be useful for your research.
NSW BDM death
1658/1889 ALLEN James age 86 years died Sydney
Sydney Morning 24 Oct 1889 p1
https://trove.nla.gov.au/newspaper/article/13746676?ALLEN. —October 23, at his daughter's residence, Carlton House, Surry Hills, James Allen, formerly of her Majesty's Royal Horse Artillery, Woolwich, England, in the 87th year of his age.
Sydney Morning Herald 25 Oct 1889 p12
https://trove.nla.gov.au/newspaper/article/13746960?THE FRIENDS of Mr. and Mrs. CHAWLOR are respectfully invited to attend the Funeral of the late
Mr. JAMES ALLEN; to move from Carlton House, No. 12, Bellevue-street, Surry Hills, THIS (Friday) AFTERNOON, at half-past 1 o'clock, for the Necropolis.
(I think this is a clumsy effort at CHANILOR)