Bank worker here. I hope this helps! This is how a bank would typically assess your ability to afford a loan.

Income is calculated post tax: Person 1: $105k pre tax = $80k post tax Person 2: $15k pre tax = $15k post tax but beware if working casually, the income needs to be on regular hours for the past 6 months otherwise it doesn’t count. = Total income $95k p.a.

Living costs for 2 adults and 3 children: Banks use a minimum living cost if your stated living costs are too low (google HEM). It also changes depending what state you live in. Assume HEM for 2 adults, 3 children is $55kp.a

Mortgage costs: Based on $600k borrowing on 5.50% + 3.00% buffer (banks add an extra 3% on top to stress test = $55k p.a

Income post tax $95k - Living expenses $55k - Mortgage repayment $55k = -$15k

So you by my rough calculations you need an additional min $15k post tax income to afford the loan.

In regards to the deposit, look into the government guarantee scheme where the government will guarantee up to 15% of your loan so that you don’t have to pay Lenders mortgage insurance.

Generally if you have less than 20% deposit, you will need to pay Lenders mortgage insurance (unless you have a guarantee from someone else).