How much profit does a developer want from a project?

I have the unenviable task of costing a development project for my father. He has a 1350sqm block 30m x 45m and I am trying to estimate how much profit each dwelling will realise when sold.
We need to do this as a JV, as my dad has no way to get this finance on his meager super (he is 73 years old). He would like to keep TWO Single story dwellings for himself.

Here is what I have come up with so far, bare in mind I am a COMPLETE novice:

1.The no of dwellings I think will fit is 6 (mix of ss and ds)
2.The block has a mish-mash of hoarders rubbish, giant shed made of asbestos, rundown 2br house with bungalow = expensive demolition.
3.My estimate is based on a fictional 819sqm total building area, and $1500/sqm cost guide leading to a whopping $1228500 plus the addition of
Subdividing 6 allotments $30k
Bulldozing $30k
Plans/Permits $60k
Services: Gas, Elec, Water $30k
So, in addition to the construction costs, I have to factor in a further $150k, grand total $1,378,500.

Now this block is in Croydon VIC, walking distance from main St, trains, bus stop literally at the doorstep, 5 mins from Eastlands shopping centre and Eastlink Tollway.

I have to figure out how much the developer wants to make on each unit for them to go ahead with it. After all, the cost is quite a nip in the pants. Also how long would all this take to build? I also presume it will need a strata title and costs involved with that?
Many thanks for all your helpful comments.