Over a beer one day I asked this question to an experianced CASA FOI.
Scanario 1:
Money is no object. Husband buys a Gulfstream G800, wife is the co-pilot. Both hold PPL/IR-ME, MCC, type rating, class 2 medical. Aircraft is registered to the husband in private category and used as family bus.All other training is done as necessary.
Answer: Perfectly legal. - it's a private operation. No AOC required
Scanario 2
For longer flights the couple takes along the butler & garder (both full time emplyees of the household)....who just happen to have PPL/IR-MEA, class 2 medical and a type rating. etc etc etc.
Answer : No idea., CASA probably doesn't have a reg for this - do CASA do private rulings like the tax office does?
Scanario3:
Can a Cessna skycourier, which is certified for single pilot in cargo operations (eg Fedex), carry 18 pax in a private operation (same as above) but with single pilot.