Hello, Elizabeth,
The Disney Cruise Line's Alaskan itineraries are my family's favorites. Oh boy! What an adventure it is to cruise to Alaska. On our family's first cruise, our days were so jam-packed that, even with the Port Adventures designated as "mild" activity level, we felt a bit tired at the end of the day. In fact, our youngest would often fall asleep at the dinner table each night. At the very least, we had no trouble sleeping well and resting up for a new day of adventure the next day!
In general, the activity level of each of the Alaskan Port Adventures indicates approximately how much physical exertion you can expect to be required. When our family did the Saxman Native Village Port Adventure, it involved leisurely bus rides through Ketchikan with minimal walking. We loved the Liarsville Gold Rush Trail Camp & Salmon Bake Featuring Exclusive Disney Character Experience in the port of Skagway. The "moderate" activity level seemed to be related to needing to stand for some time at the gold panning stations as well as some short walking over somewhat uneven terrain. An "Athletic" experience such as the Adventure Park and Ropes Course at Icy Strait Point is an example of something that would require significant mobility, agility, balance, and probably endurance.
For each of the Port Adventures, I recommend carefully reading the "Know Before You Go" section of the excursion descriptions. There, you'll find more specific information about activity levels required and any important restrictions that may apply, including any age restrictions. After reviewing that information, I would recommend consulting with competent advisors or medical professionals caring for any members of your party who may have health conditions that could make certain excursions more difficult to enjoy. To accommodate different ability levels and interests, it may be appropriate to choose separate Port Adventures for different groups from your party in any given port. When you gather together again during your rotational dining experience in the evening, it would probably be enjoyable to compare notes with each other as you talk about your different experiences.
Whichever Port Adventures you choose, I'm confident you will have an amazing time on your cruise, Elizabeth. Even when you are not out on an excursion, you will likely love seeing the gorgeous scenery go by as your ship sails through Southeast Alaska's Inside Passage. We even spotted some whales while enjoying a walk outside on deck 4 during our last cruise to Alaska.
Have a wonderful time, Elizabeth!
~Tony