Long time no speak. I really feel for you and your family. Like others have said, please keep your chin up. It is a rollercoaster, but if you stick with it, then it will be worth it. I have also heard good things about 'Go Matilda', and I would definetly consult someone like them for advise.
You mentioned checking out the 457 visa as an option. We came on a 457, and after a few months it is relatively straightforward (and cheapish) to change it to a PR visa. It does mean that you are not entitled to any government financial help whilst on the 457, but it does not add or detract how secure we felt being here.