Depending on how old these teens are you may wish to design in a private side trip just for them. Give them a day or two to explore and travel on their own via rail. It can be a great experience for both parties (some mom & dad time) and give them some grownup experience while being a short distance away.
Start in City A and on your way to City B the group splits of parents and teens going to 2 relatively nearby cities that connect to city B. This all depends on the age and how comfortable you feel with the idea.