I've cruised to Alaska in Sept. a couple of times, and have been very fortunate to have mostly excellent weather. You do have to pack so you can layer your clothing for warmth if necessary.
From the little bit you're told us about yourselves, I would eliminate Holland America. That time of year you won't find tons of kids on Alaska cruises, but as good as Holland America is, it will certainly be an older demographic on HAL.
Princess is more of a mix, but will still trend to a bit of an older crowd.
NCL will likely be the best blend as far as the demographic. I also love the choices of different restaurants on NCL, and in Alaska it's nice because you can dine whenever you want, and don't have to be rushing back from busy days in port to get ready for formal nights, etc. Casual dress is the order of the day everyday.
As far as suites VS balcony cabins. Suites are naturally great, but if the cost difference is substantial I'd opt for the balcony cabin, and spend the savings on some of the "adventure excursions" in Alaska... like the helicopter ride, landing on a glacier, and dog sledding, or going up to watch the bears feeding on salmon in the river, or some of the other flight-seeing adventures.