Fredie Sorry for not getting back sooner but I had to wait until I had the chance to check at the Genealogy Society. Didn't find any of yours listed on the 2000 electoral roll.[ voting is compulsory in Australia and everyone is supposed to register their names]
Found the Funeral Record for Monty Thomas James Austin who d 6 Dec 1960 in Brisbane. He was buried at The Lutwyche Cemetery [ in Brisbane] His next of kin was listed as his wife, Gloria May Irene Austin and their address was 68 Ryder St Wynnum North [ Brisbane] Appears that his first wife either died or they divorced. He died at the Greenslopes Repatriation Hospital and was a TPI pensioner. He was probably injured during his war service in the RAAF.
Couldn't find any more on his sister. If Monty had any children, they would be listed on his death certificate. There maybe also some clues in the newspaper Funeral Notice which was published in the Courier - Mail in the Thursday edition after his death.Unfortunately, I can't get to the Library to check this for you.