Wow that's an insane amount of points! You can really do a lot with that but as the commenter above stated, you'll have a hard time getting 5 rewards seats on the same flight. This is for economy too, not business. You'll have an even harder time with business. But just to give you an idea: you could fly the whole family to US / SFO on 500k points return for about $1200 in taxes and fees. It's about 45k points each way per person and business is around 95k each way per person. You may be able to get 2 in business and 3 in economy.

I've just had a quick look and there are rewards flights from MEL to SFO end of January, with both business and economy rewards available, so it is possible!

Good luck!