I don’t know anything about the by-laws in Australia, however your need to put a roof over the heads of your family, and your preference for an ecological solution struck something of a cord.
Here in France we have some pretty tough rules and regulations, however I was reminded of one family that achieved exactly what you are trying to achieve and ended-up with a grant to help complete the work.
Essentially, they installed a Yourte for their family, adapted to provide a small shower, toilet etc. Not only that, they installed the Yourte on land owned by the local commune.
The law concerning such matters moves very slowly here in France, unlike public interest which soon reached the local population, the local press, and eventually the national press.
It is interesting to note that the emphasis was always on ecological housing, low energy, protecting the environment etc,.
Towards the end of last year, with a couple of inches of snow on the ground, the family and their Yourte were visited by the French Minister for Ecology who gave her full support for the installation.
The last I heard there were several Yourte’s installed and a log cabin – all with the blessing of the French government.
Perhaps one of those occasions when the problem became the solution?
From the answer’s you’ve received so far, it would appear that you may well face problems whatever you do.
So, how radical are you feeling???
Very best of luck,