As others have already mentioned, it would be very difficult to gather up enough QP invites for your party and the Novotel is rather expensive. There is a Brisbane public bus 308 service which runs from Toombul Interchange (buses and train) to Airport Village where the hotel is located, as well as a free Airport Village to International and Domestic terminal shuttle service, but since you are arriving into Brisbane rather late these services would be winding up for the day.
Personally, i think booking a hotel in Brisbane is rather unnecessary and would instead spend the rest of the day around Southbank. Take the train one or two stops from Roma St station to South Brisbane or Southbank station (last time I was on a Sunlander we had free travel to anywhere on the QR CityTrain network on the same day of travel but if this is still the case I doubt it would apply to the airport line as its a private line).
Leave your luggage behind at a hire locker at either Roma St station or Stanley St Plaza in Southbank. If you get in early enough you might even want to take your kids for a swim at Southbank beach. Think the beach closes around 5 or 6pm this time of year. There are shower facilities at Stanley St Plaza for you to use. You can charge mobile phones, laptops etc at the State Library (closes 8pm Mon to Thurs). Have some dinner, drinks, wander around the parklands etc then make your way back to International Terminal on the Airtrain. The last Airtrain leaves South Brisbane at 9:01pm and arrives at International Terminal at about 9:30pm which should be well within your 3hr checkin window. Alternatively, a maxicab should cost about $57 from Southbank. With the money you save not having to book a hotel, you might even want to treat yourselves to a ride on the Wheel of Brisbane.
Of course, if you prefer the comfort of having a hotel room then by all means consider that too.