did you ask over in the tandem section? Im sure you will get much better informed answers from real experience regarding climbing steep stuff (and especially with a trailer too) and it being doeable, not to mention long downhill experience regarding braking (again, especially with a trailer)
I suspect asking us single bikers questions is like tourers asking questions about climbing to a bunch of roadies on 17 lb bikes.
all the best getting some answers from folks who have actually pulled a tandem plus stuff up mountains (hey, just had a thought, what about asking the mom of that Alaska-SAmerica family, NancyV, didnt they have a tandem and a trailer??)