I cant help you with the legal side but I did make an offer on a duplex this week in the hunter valley NSW. I thought they were such an easy clever design that I am now thinking about buying a block of land and building the same thing myself.
It looks to me like they were 2x 2 bedroom granny flat type units, mirror image, side by side with a common double car port roof between them.
Facing the street so the driveway came straight up and under the carport. They had solar hot water and water tanks out the rear.
They were made out of hardyplank and colourbond. were tiled floor in living area and kitchen. very neat and tidy. only 4 years old.
I’m trying to research similar ones on the net to get some idea of prices. I dont think they would be over a 100k though.
if they fit into my budget I think it would be the way to go for me. Small cheap building but with a double income. There is plenty of call for that sort of rental.

Anyway just thought I’d pass on my idea. Good luck with it all. Let me know if you find anything on the net like it.

Maree-bradros What sorts of things qualified? I have an old house and didn’t think it would be worth it.

I don't  understand?   So how do I qualify for a 450k new home which costs me $80 a week.   I too have lots of equity and a salary of over $70k     I had no problem.   Why don't they use your home as security?       Why don't you give a financ broker a go?