Would like to take our family of 5 adults and 4 teenage boys (grandchildren) on a "special" celebration trip in the summer of 2015. Activities important. Beach not necessary. Ideas?

Idaho Rocky Mountain Ranch.

I know exactly where you should go.

Where are you traveling from?

How do you want to travel - plane, train, bus, car?

How far are you willing to travel?

What types of activities interest the adults in your group?

What type of activities interest the teenagers in your group?

What type of accommodations do you want - motel/hotel, full service resort, villa, cabin, condo, etc.?????

How long a trip are you planning?

What is your budget for accommodations, food, activities???

Without further information from you, there's an endless list of possibilities...

Three generations of our family went to Kauai and had a great time.

As others have suggested there are endless possibilities with no information available from the OP.
An all inclusive Club Med?
Atlantis in the Bahamas?
Dude ranch in the Grand Tetons?
Who knows.