Do you plan on spending extra time before or after the cruise for a land tour to Denali? If not, unless you really want to see College Fjords, I would suggest doing the inside passage round trip from Vancouver or Seattle. We prefered Vancouver because they sail inside of Vancouver island. Seattle cruises outside of Vancouver island however still has beautiful scenery. This might eliminate Princess for you however because I'm not sure that they do the round trips.
I notice that the Volendam visits Glacier Bay and Tracy Arm (Sawyer Glaciers). That's a great route IMHO.
We sailed the Zaandam to Alaska a few years ago and she was a great ship. In Alaska you'll find a younger crowd of cruisers, even on HAL. If you travel after school's out you'll also find quite a few kids on the ship, so if your teens do want to socialize with kids there age they won't have any problems. There is also a nice teen club from what we could see.
It seems that when the Zuiderdam launched a while ago that there were a lot of complaints as mentioned above. Not so much anymore from what I read. They've probably ironed out the problems.
As a whole the cruise, no matter which line you choose, will be more low key than a Caribbean cruise or Mexican Riviera cruise. No bands playing at the pools. No pool games.
IMHO your decision to visit Glacier Bay is a good one. This is an awsome place to see. We enjoyed our trips there more than Hubbard Glacier.......not that Hubbard isn't spectacular too.
Good luck in your decision making. That's part of the fun of a cruise I think.
