Dan, a few comments to add to the others. I agree with the previous post that suggested you might want to stop by ETBD headquarters and talk to the tour staff. It might be an idea to take your teenagers along as well, as they'll be more "on board" with decisions if they have some input. The visit might provide some enthusiasm also, once they hear about all the interesting locations they'll be visiting on the tour.
The Family Europe in 14-days would probably be the best choice, as there could be others the same age, so they won't feel isolated in a group of older people. The ETBD staff could provide a better idea on what type of "mix" they normally get on the family tours.
They should be aware that they'll need to be a bit "flexible" on the tour, and also concerning dietary matters. I'm sure the experience would be interesting for them. BTW, I have three boys (now grown), so I know what the "teenage years" are like!
Happy travels!