Hi,
Your G'ma, Ruby Cundith/Harington, was my Dad's first cousin and her family lived in Gympie. I have looked at my notes and I have stuff which you may already know. Dorothy J divorced John H November 1918 - from notice in Sydney Morning Herald. Dorothy remarried ?Fraser. Her funeral notice was in Courier Mail, Brisbane.
She had a business - dressmaking? - in posh Rothwell's arcade, Brisbane. (from Directories) She lived Dean St Toowong Brisbane. Reg/Claude could have gone to private school nearby.
Today, I found a Dorothy Harington went insolvent in 1921 - see Q State Archives. Also I googled RWCH's full name and found a discussion of his WW2 details plus more.
We felt we could have gone a bit further but did not have the money to spend on documents eg divorce papers. Hope this is helpful. Gazania