Finance a knock-down, sub-divide & build 2 semi-detached in Adelaide

Hi All
We have a IP that we are in the process of looking to knock down and build 2 attached dwellings.
Have already engaged suveyor for sub-division process and have designs & first deposit paid with builder, awaiting fixed price contract
as I type this hopefully only 1-2 wks away.
My problem lies with the financing structure and approvals, being new to this we have moved forward to this point on some otherwise questionable advice that has me now trying to get the correct advice.
Firstly we are doing this as a J.V with my mother & step-father, he wants to retire asap due to health so we are trying to make happen quickly. LVR will be about 75-78 %, total outlay about 1.15m – conservative return 1.35m ( current market ) Total income for serviceability approx 230k between all 4 of us.

On the advice of our broker & builders sales rep we re-tenanted the property for 6 months about 8 wks ago,  2 weeks later our broker informs me that we need the deposited plan number for sub-division, council approval, plans and contracts from builder. No problems – I ring our surveyor for DP number he informs me we won't get this till house is demo'd & final survey lodged with LTO. 

Now heres were I get a bit lost, can't get finance approval without DP Number, can't get DP Number without knocking house down and I'm a bit reluctant to knock house not knowing if we can go forward.

I believed we would be able to get finance approved subject to ( sub-div dP number ) which would have then allowed us to move forward with a little security, it seems a little unrealistic to have to demo the house without anyway of knowing if finance will be approved.

 Is this normal procedure with the banks ? Is there a way around it ? Does anybody know which finance institute in SA would be best one to approach ?

 We need the seperate title valuation to achieve the LVR, we are happy to move forward on shortened valuation due to 2 houses on one title as long as we can go back to bank when we have 2 dp numbers for re-evaluation.

I thank you all in advance for taking the time to read this and thank anyone in advance for any assistance you can give us, please ask any questions that may help you answer  as we really need the Help !!!

Cheers Matt