Looks like there's no discount for second child, but third gets 50%. If you look at those numbers, the bill is OVER 60k (the discount would, obviously, apply to the 'cheapest' child.
http://www.cgs.vic.edu.au/wp-content/uploads/CGS-Fees_Charges_20154.pdf
For those unable or too lazy! to paste link into their browser, it's over 20k for a year of prep, rising steadily to 25k in year 6, and 28k in year 12.
Do the children go to Camberwell Grammar? A slightly surprising choice, somehow.
This is tacky and pure speculation - but my bet is they are not financially independent and have some family money. I would be surprised if their properties, school fees, and lifestyle was paid for 100% with his income.
They would need to be saving for the future, and doing things like travelling to Boston to run in a marathon is very expensive. It's not really something a one income family with three kids in private school would do.
I agree with this. I don't think Elisa would have opted to become a SAHM unless she'd had some (family) money of her own behind her.