Oh I forgot to mention that when I searched for Evelyn Castles on the electoral rolls on ancestry there was a Kerry Michael Castles living at the same address (in Quilpie) as Evelyn & her husband Reg in 1977 & 1980. However, I don't know if Kerry was a son or some other relative of Evelyn & Reg, as he is not listed as a child of Evelyn's in her newspaper death notice. Are you able to find out how he fits into the family?
cheers, John