You're taking 2 teenagers to Japan and not spending time in Tokyo??? Big mistake!
One night in Kyoto and one night in Hiroshima, a day in Nara or Osaka and the rest in Tokyo - that's pretty much what I would do. Unless these are unconventional teenagers, take them to see youth-central Shibuya, futuristic Odaiba, Akihabara electronic city and the list goes on forever. Are these girls? I'm sure they would love shopping for clothes in UNIQLO and to wander around in the fashion district of Harajuku.
Take a look at my blog (see signature below) for more ideas.