I can highly recommend Melbourne! We've been in Melbourne for something like 4 or 5 years now and we love it here.
The government has this website which provides all the information you need regarding the Australian school system:
https://www.studyinaustralia.gov.au/english/australian-education/education-system
In general all classes are given in English, although there's some schools that offer classes in other languages too. Finding one that teaches in Dutch will be a big challenge though. I can't imagine they exist. The Dutch have a bit of a reputation here for being good at English.
In addition to that, Melbourne is pretty big so there's every chance that even if there's a school that teaches classes in Dutch, it's more than an hour away from your husband's work. Deciding to live in the north, east, south or west of Melbourne is somewhat similar to deciding to live in Haarlem, Purmerend or Almere. Distances are smaller, but you'll spend just as long in the car due to traffic being slower.
Honestly, your best bet is to just teach your children English. Just start with speaking English at home, reading books in English, watch TV without subtitles. Things like that. They don't have to be perfect at it when they come here, just good enough to get them going.
Not only will that make finding a school and a place to live way easier, it'll also help them fit in and make friends. Australians in my experience are really inviting and open to people that are serious about being here. If they can tell you're only there temporarily and aren't really making an effort to fit in, they'll be friendly but they generally won't be as welcoming.
Ps. Almost everyone here is/speaks Dutch, so feel free to continue the conversation in Dutch
