This could be a tough order- SkyTeam (which includes Delta and Korean Air) has notoriously poor coverage in New Zealand, so you might need to buy a separate ticket with another alliance to get from AKL-SYD on your way home. But that's doable if you're willing to pick up your luggage in SYD and re-check it with Delta.

The bigger problem is that getting a D1 award seat from ATL-SYD roundtrip will require 765,000 miles... per person, so more than 1.5 million miles for both of you.

You can try booking the open-jaw flight with Korean Air (which has some flights to AKL) but it will still be close to $8000 per person. United also has flights into/out of Australia and NZ for around $8000 in Polaris or $5000 in Premium Economy.

Have a great trip! What a marvelous adventure.