I can see the nanny as staff, but not the In-Laws.
That's funny, George: I see it exactly in the reverse.
As far as the in-laws are concerned, there is room on the plane and as long as they pay economical fare, like the PM and his wife and kids, I see no problem with that as they are vacationing together (in fact, as long as everybody pays commercial fare, and considering that the PM must
travel that way, it makes more money for the government for that particular flight, so actually a plus, not a minus.
The nanny, on the other hand, is federal employee, hired at taxpayer's expense specifically to look after the kids if and when the PM and his wife are both required for official public duties (not of the PM's wife to have a personal job - in which case she should pay for the nanny). They are not required to attend any such duties during their holiday - so the nanny's presence has no other function than their personal convenience (romantic supper without the kids?). They should pay for that convenience and if her salary is fixed pay, you then do an apportionment and charge them for the service.
After all, when they are on holiday is when the nanny should also be on her holiday. Otherwise, when she wants to take her holidays, we end up paying for a temp replacement over and above her cost. That's how people that have nannies usually work: we go on holiday - you go on holiday.
Well, if our flight attendant posting was a full trade, we'd end up like the RAAF with their Crew Attendants on 33 and 34 Sqns:
Actually, Dimsum, we used to have flight attendants as a trade in the CAF when the Air Force operated the service flights on Boeings 707. And they were not bad looking people.