Hi. I have no experience of this but have been to Australia many times.
I don't think it matters where in the world this is, the issues would be the same, except Australia and NZ are furthest away therefore you have to plan well.
Just a few questions:
Why do you stay a six hour drive away? I know some parts of Australia are remote but even if you can't physically stay with them (there must be good reasons?) surely there would be something closer?
The father is entitled to time with his daughter, and she with him so I don't see the issue that your granddaughter will be away from ten days, you don't say how old she is.
You will still be spending time with your daughter and I would make the most of that time with her. You can still be in touch with your GD by phone etc?
I have lots of family and friends in Aus and they all realise we can't get to see everyone on such a trip- it isn't geographically possible.
You have a choice though, to go when your GD isn't visiting her dad, but I can see that may present difficulties too.
This is my advice, to go anyway and make the most of time with your family members. For me it is a quality not quantity thing.