I've been on three RS tours with teenagers and/or college students (Paris, Rome, and Venice/Florence/Rome). Everyone meshed well on these tours. As others have said, social skills are pretty important--I don't mean being an extrovert--I mean being polite, patient, and able to make basic conversation with tour members of all ages. Also, are your children into standing and listening to a guide speak about history, architecture, or art? As Rick says, no grumps. The only grumping can take place in the hotel room amongst your own family.
As mentioned above, you can skip some meals or tour activities, but please let your guide know in advance. Group dinners typically come with a choice of three entrees. For example, in Paris that might be chicken, fish, or vegetarian. Quirky hotel rooms (or things not exactly like they are at home) are part of the adventure of travel, Life experience, in my opinion. Definitely ask them their thoughts, and good luck with your travel plans!