Kiwi in London 11 years, German partner, kids on the horizon. How did you decide where to settle?

I'm 38, from New Zealand, and have been in London for 11 years. My partner is 28 and German. We've been together two years, are discussing plans (and possibly kids) in the next 2–3 years, and have started the "where would we actually live/raise them" conversation. Also a bit of scenario planning (I know - 'man plans & god laughs' etc.) but feel it's prudent to be aligned on 'if this, then that' (e.g. her parent/s are ill, then we look at X).

Where we're at:

• I grew up in a small NZ city and had one base for 25 years, with friends I still have now. I want that stability for our kids and really valued my upbringing: one hometown, same school, best friends for life made who I am lucky enough to see often in different places now (left when I was 27). Would prefer not to move every few years (if possible)
• Neither of us wants to raise kids in our hometowns. Mine is too small for us, bit boring and she'd be a (very) long way from her family and in a fairly homogenous sort of environment. We couldn't see ourselves in Berlin (her parents & brother there for now), despite absolutely loving visiting.
• Australia (Melbourne or Sydney) keeps coming up as a possible option. My brother is there, a lot of my friends have ended up there, and it's three hours from my parents. She's open to it, but it puts her roughly a day's travel from hers.
• Both sets of parents are healthy now, but mine are heading towards 70. Hers mid 60's. I'm very aware that at some point one of us will need to be near an ageing parent on the other side of the world.
• My, ours and her London friend group is always changing (as people move home or have kids, suburbs etc.) The expat adventure changed has slowly but surely changed into 'life' that feels different now. London could work but it doesn't feel like a forever place.
• We're fortunate to have transferable jobs and savings/resources.

For those in cross-country couples with kids:

1. How did you choose the base, and do you both still feel it was fair?
2. How have you handled a parent getting sick far away? What actually worked?
3. If you raised kids away from both families, how did they turn out on the "belonging" front?
4. Anyone done London to Melbourne/Sydney with a European partner? How was it for them, especially visas and distance from their family?

Not looking for one right answer, just how people have actually made this work. Very conscious we are blessed to be citizens of the world - so a nice, but tricky, problem to have and many of my oldest friends are back in New Zealand or Australia.