I know this isn't what you asked so pls ignore if inappropriate, but if you're looking for one last major trip before embarking on kids might I suggest choosing one that is way more suitable without kids than with?

Australia in general and almost all the places you have mentioned are very easy places to travel with children. I've done a lot of it. Long flights are not really a big issue tbh, the only possibly problematic age is the 1-2 year.

I don't know where else you've been, but there are many worthwhile places that are very challenging to visit with small kids that would be a great choice to hit before littles arrive. India, Nepal for example; parts of S America. The places where it's potentially a major issue if they drink the bathwater (Amans included). I speak as someone who has done a good deal of lux travel both pre-kids and over the last 10 years during which we have accumulated several of them; happy to discuss in detail.

Fully acknowledge the Australia decision may be done and dusted in which case great advice above, and enjoy!