There is a birth in Collingwood in 1890 of Wm Hy Ernest RILEY, also registered under his mother's surname of BUCKLEY (reg 2449R). His father is shown as Wm Hy RILEY, mother Catherine BUCKLEY.
The newspaper notices (NLA Trove) indicate his wife was in England and his mother in NSW:
The Sydney Morning Herald, Saturday 1 December 1917, p.12
RILEY. -Killed in action, November 7, 1917, Private William Henry Ernest (Son) Riley, 2nd Battalion, aged 28 years. Inserted by his loving wife, Nellie[?](England) and children Irene and Grace.
Other notices are from his mother and siblings, Joseph, Leslie, Grace, and Irene of 25 Boundary St, Redfern; John & Lena Riley; sister Edith Tanner and her husband Henry, of Camperdown; sister Elsie Moffitt and her husband Fred.
His wife must have been nee CROOK as there is a notice from the Crook family stating he was the son-in-law of E. Crook, brother-in-law of Mrs R. Johnson, R. Crook & W.H. Crook, of Erskineville.
It seems he was known as Harry and also Sonny or Son. Other notices from cousins! So he did have a big family.
here's his marriage in NSW:
303/1911 RILEY WILLIAM H / CROOK EMILY S / SYDNEY
wife Emily's birth?
37295/1891 CROOK EMILY S / ROBERT H / ELIZABETH / WATERLOO
Daughter Irene E b. 1911 Sydney
Births of siblings in St Peters, NSW (except Jos):
Joseph 1895 Redfern
Leslie B 1898
Irene N 1904
Possible death of father Wm Hy RILEY in 1905 in St Peters, son of John & Mary (reg 6746).
Parents marriage (explains why Wm Hy Ernest was also reg as BUCKLEY):
259/1895 RILEY WILLIAM H / BUCKLEY KATE / SYDNEY
Wm Hy Ernest's sister Edith Martha Mary was born in Collingwood in 1888 (reg under both surnames). Can't find sister Elsie. Assumning the John in notices was a brother, possible birth in Victoria in 1879, as BUCKLEY, father not stated.