I feel like I'm tilting at Gods here, but Regional pride will prevail and I must take exception to Pumaman's comment:
"Cairns is ok, it doesn't have a beach but it does have some tourist activites like the bleached barrier reef, and the weather should be good. Port Douglas is probably nicer but smaller."
Fair bite of the pineapple doughnut! Cairns city doesn't have a beach, unless you count the fabulous man-made city lagoon, (Google it) but what about the northern suburbs collectively known as the "Northern Beaches"? Namely; Machans Beach, Holloways Beach, Yorkey's, Trinity Beach, Kewarra Beach, Clifton Beach (my home) and Palm Cove? 5 minutes from my door I can walk along pristine sand for half an hour until I get to Palm Cove where I have breakfast under the 200 year-old paperbark trees; trees so treasured that the local buildings are built around them.
Regarding the Great Barrier Reef: Sure some reefs have suffered bleaching, but not the tourist destinations. "My Aquarium", as I call it, is largely unspoilt, and still a major world wonder. Just to give you an idea of its size, when you fly north-west out of Brisbane, after 20 minutes you pass Lady Musgrave Island - the southernmost part of the reef. If you flew for the next 3 and a half hours until you hit Niugini, you would still be over it. Are you really going to come to OZ and NOT see the barrier reef?
Other tourist attactions include the Skyrail rainforest experience, Tjapukai indiginous culture extravaganza, cold beer and nice steak. A word of warning though, if you see water, assume crocadile. Read the signs and obey. They really are out there.
Do you really need accommodation for 16+, or would 4 rooms of 4 suffice, or any other mathematical combination?