Potential to build a duplex in Greenacre

Hi everyone,

I'm here to try figure out what can be done with some of my family assets and the costs invovled in doing some things.

My brother owns a property in the South West and my sister owns a property in the inner west. I'm looking to buy a large corner block in Greenacre. The block is approximately 970 square meters so I think there is potential to do one of three things:

1) Keep existing house, subdivide the block and build another detached dwelling behind it; or
2) Knock down the existing house and build a duplex; or
3) Keep existing house, subdivide, and build a duplex behind it.

I was planning on buying this property in Greenacre, and somehow, use my brothers property and my sisters property as a 'guarantee' to get a construction loan or something but I don't know if this is the best option.

Potentially, another option might be to buy the Greenacre property under a company, and then transfer the other two properties into the company name so that the loan can be guaranteed within the one company. What are the cost involved of transferring title from an individual to a company?

And just generally, what would be a good way to structure this?

If anyone knows of any good accountants/surveyors/financial advisers, please let me know as I definitely need some expert advice.

Regards