Our family tours have not been as ambitious as your plans.
Have toured with our teenage son and a year ago with our 9 yo on a tandem and this past summer
with him now as a ten yo on a solo bike.
Could list all the usual things like hydration and bike fit [our teenage surprised us how much he grew in just a few months- more than one bike size], etc.
There is one lesson we were slow to learn on our first trip with our teenager - the ride was not our ride, but our child's ride. Once you sync with that and really follow that guideline- the trip for everyone will be great. Good Luck.