Well if your dad needs cash for biz.
I'm assuming you and sis are helping for it.

30% of downpayment not needed. Just sign documents as if its been paid by you/sis to dad.
Generally it will be only 70% loan for purchase price. 85% possible, but most cases hard. Nevertheless, try.

If you plan to build a house, you need house/building plan approved via correct channels ie. architect, majlis, etc.
This can be submitted to bank for loan purpose.
Again bank typically offers 70% loan from BQ value.

Take note there is clause within residential land purchase in bank loan agreement that house must be build within 10 years from date of land purchase. But if payment is prompt and no issues, bank will not kacau.

Good luck!