G'day Lookup,
Although you're asked the question about a stop in NW Australia and the responses are framed that way, there's an important point that's not been mentioned and may impact you and particularly your pax.
Quarantine and your catering. AQIS will definitely take part, if not all, of your catering as it'll be your first Australian port of call. All fresh food(Fruit and Veg) will definitely be taken, other products(ie hot meals, juices, etc.) maybe, if fact probably will be, taken from the aircraft. Best if you want a complete list to look up the AQIS site or contact them to find out what will be taken off the aircraft. You probably won't be able to get a restock at these ports unless you time your arrival to when the supermarkets, cafes or hotels are open, as Broome and Port Hedland don't have FBO's, plus you'll probably have to go off airport to source these yourselves which will be a hassle and an extended turnaround. AQIS will leave stuff like biscuits(cookies), chocolates, chips(crisps), muesli(granola) bars and other processed foods but your pax may want more than that. Port Hedland does have handlers if you want them but I'm not sure if they can help you out with catering; there's also a Terminal café, if it's open when you go through, but it may not have what your pax want to eat.
I'd have a look at Bali(WADD). It's a little off the direct track but it has an ILS if the weather's bad and it now has a dedicated Biz jet apron(so new it's not shown on the Jep 10-9 yet, FYI it's south of the runway) with an FBO, that I believe Execujet is operating. Personally, I'd recommend Mr Dude and his team, can't remember the company's full name but it's "***** Biomantra", Universal uses them at present. The Indonesians won't touch your catering, or give you any hassle at all, and if you update Mr Dude with an accurate arrival time you'll probably find that the fuel will be going in the aircraft before the engines have fully wound down; I reckon you'll be able to do a turn in well under an hour, probably 30 to 45 minutes. You could also get a lav/water service, ice or additional catering if you want.
Of course, then your pax won't be able to just grab their bags and go in Sydney, but usually you'll be cleared in well under 30 minutes in either Sydney FBO, I'd guess 10-20 minutes is about normal.
Just my 2 cents worth.
The Caveman