I live in Kenai, Alaska and would say your outline looks pretty fun! Denali is worth going to because it's Denali and you should be there at least once in your life if given the opportunity. You are also guaranteed some great wildlife viewing. Fairbanks is an interesting place as well although it's really flat and very hot this time of the year. Most people flock to Fairbanks in the winter because of the amazing opportunities for Aurora-Gazing and the fact that it also takes almost a day to drive there from Anchorage (or an all-day train ride). There should also be some good berry picking opportunities there at the time of your visit as well. The railroad is a great way to travel if you are not in hurry and don't mind the cost of a ticket. Going south there are a bunch of options as well! If you guys wanna do kayaking there are excellent options out of Seward to explore Resurrection bay. They have a lot of different things going on for renting to tours, solo, or camping included trips. There are also some great day-hiking options in Seward and then the highway from Seward to Soldotna/Kenai is littered with good short multi-hour to long multi-day hikes. If you are into the water-scene and are feeling a little "extreme" I would HIGHLY recommend white-water rafting Six-Mile river in Hope which is just south of Anchorage. They are very fun but they are also class 5 rapids. They were my first white-water experience so beginners can handle it but you will get physical with the water haha
I'm realizing I'm getting a little rambly, as you can tell, I'm a pretty big fan of where I'm from. It's almost impossible to come here and not have an amazing time so as long as you guys keep your eyes out and explore you should be ok.