As this appears to be a case of the parents killing their teenage children, and then commit suicide, it's eerily similar to a case that happened in Sweden in 2018. In that case the parents, in consensus, agreed to killing their daughters, 11 and 14 years old, and then themselves. Both girls had been suffering from myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) for several years, and the parents couldn't see any other solution, even as they got all the help the school, the healthcare, and social security system could offer. I don't know how it's in Australia, but in Sweden I would say that there would't have been that much of a financial burden for a family with chronically ill children, as most, if not all, the aid they recieved was free of cost for the family.