I started by looking for marriages between a male Ivison and a female Warnes and followed up by by looking for an Ivison in passenger lists for Australia 1927. I had a stroke of luck when Robert, Bertha and your mother Margaret Audrey turned up. Even better was that they were accompanied by George Alfred Warnes, his wife and son! I worked backwards from him - if that makes any sense! I've started sending you some files. Hope you enjoy their content.