Hi HB mom,
Unless you have some excursions planned for a glacier, I'd leave the real warm jackets at home and pack lighter ones, plenty of t-shirts and sweat shirts and still include that rain gear, you can almost always expect that at some point during the cruise. I threw in 2 pairs of shorts and believe it or not, I did wear them a few afternoons and we were up there the first week in Sept.
Have Fun!