Do you want to stay in US or go international?
Domestically, you may want to consider Vail or Key West! Will provide details if you like.
Internationally, there are so many choices, but you might consider a place where there is something for everyone to do. Europe, is always my first choice with a foursome of such different ages. You could all do something unique during the day and then share experiences over dinner. Good luck,
I think you will get some great ideas!
Went to Australia Oct 08. Used points to stay in Sydney and Surfer's Paradise. Stay at Sydney Circular Quay. The location is perfect - a block away from the water. The concierge lounge was average. Also used points for a stay at Surfers. The location isnt as good as the courtyard - is a bit of a walk to get to the beach or downtown, but its a lovely place. Since food is so expensive in Australia (at least it was when the exchange rate was bad), we used points to buy "Dinner for 2" certificates to be used in the Marriott Restauraunts. They provide a good deal and everything is included, except alcohol.
I had some issues at the Melbourne Marriott. Stayed there for 24 nights in Feb 08, wouldnt stay there again due to them making a mistake and failing to correct it. In Oct, I stayed at the Grand Hyatt instead - absolute BEST hotel ever!!
Our 27-day trip to Australia in Sept 2005 was simply wonderful. We visited Sydney (Opera House, Harbour Bridge, Bondi Beach), Melbourne (Philip's Island to see the fairy penguin parade, Geelong and The Twelve Apostles along The Great Ocean Road), Ayers' Rock (or Uluru), Coober Pedy (opal mining town in the Outback), Surfer's Paradise (only Marriott Resort in Australia), Brisbane and Cairns (Great Barrier Reef). We stayed in Marriotts in all locations except at Ayers' Rock, Coober Pedy and Cairns (there should be one here).
With respect to how many days do you need in Australia, an obvious answer: the more the better! The country is vast, liken it to the US. However 90% of Australia's population is within 20 miles of the ocean, essentially a ring of people on the coast(s). So you're going to have to make some tradeoffs. I can't imagine visiting Australia without at least 2 weeks there.
If you only have a week, you must stay in Sydney (at the Sydney Harbour Marriott). If you have two weeks, I'd stay a week in Sydney and a week in Cairns. With a third week, I'd add Surfer's Paradise. All three of these visits were different and so much fun. Note that the distance between these locations dictate that additional air travel is required within Australia.
If you'd like to discuss this further, just let me know.
The attached pictures are from Sydney, Melbourne, Surfer's Paradise and from the coast between Cairns and Port Douglas.