Alice Gay's death notice
The Argus, June 18, 1951 http://nla.gov.au/nla.news-article23060725
Here are the details of the War Service of the brothers. I have included their Service number (SN), so you can look up their full record on the National Archives, www.naa.gov.au
Gay, John Phillip McCandlish (SN 1474) Phillip as he was known, was 23 when he enlisted on July 31, 1915. He was a farm labourer, his next of kin was his mother, Alice, and he Returned to Australia April 12, 1919.
Gay, Rupert Alfred (SN 1479) Rupert was in the 1st ANZAC Cyclist Corp, and he enlisted on August 14, 1915 at the age of 21. He was labourer and his next of kin was his father, Robert. Rupert Returned to Australia June 12, 1919.
Gay, Robert (SN 5356) Robert enlisted on April 10, 1916 at the age of 18. His next of kin was his father, Robert, and his occupation was farm labourer. Robert Returned to Australia October 8, 1919. Robert was granted a soldier settler farm, you can read his file, here, on the Battle to Farm website.
A farewell was held at the Lang Lang Hall on August 30, 1915 to say goodbye to some of the local boys who had joined up - including Rupert Gay.
Lang Lang Guardian September 1, 1915. http://nla.gov.au/nla.news-article119512821
This very nationalistic and patriotic poem, written by Robert Gay, was published in the Lang Lang Guardian, June 14, 1916. I don't know if it was Robert Gay, the father or Robert Gay, the son. I suspect it was the father, as Robert Junior was only 18 in 1916.