Will your uncle meet you at the airport to hand over his truck? I'll assume extended cab to fit 4 people. Hopefully it has a topper or a bed cover to guard your luggage!
If you borrow his truck at the start, I would strongly suggest not going up to Fairbanks. Lots of extra miles put on for just a couple things that can mostly be done elsewhere. For a first trip you really have to budget your time to enjoy it and not be panic driving to get to your next stop. Plus, no matter what he says, you don't want to pile on a bunch of miles on his vehicle. One trip we took there we racked up about 2500 miles!
New idea. Fly in, have a nice lunch or dinner in Anchorage. Unwind from the flight. Drive to Wasilla and check in with family. The drive there will be eye opening for the kids. Mountains right there close enough to touch. Traffic kind of sucks but they won't notice.
Spend the night in Wasilla.You'll be tired. Lots of motel choices. 2nd day drive up to Talkeetna for the flightseeing. Walk over to the river for a nice view of Denali. (if it's out) Several good places to eat there. Hopefully you'll hit a day with no tour busses. Doubt it, but it might happen! The Talkeetna Alaskan Lodge is a nice place to stay and the view from the deck while having lunch or dinner can't be beat!
Lots of dog kennels between Wasilla and Talkeetna. Willow is sort of like "musher central". Find one to visit now or save it for later. Wave at my old cabin as you drive by.
Next day pack a lunch for everyone. Take the Hatcher Pass drive from Willow all the way through to the other side. Then drive up to the Matanuska glacier and let the kids walk around. Not much for food, that's why packing a lunch would be helpful. Come back down to Palmer and take the kids to the muskox farm or the reindeer farm if they're interested. Kids get bored with driving too much!
The next day leave early and drive down the inlet to Girdwood. Be very traffic aware on that road! Take the kids on the tram to the top of the ski slope. Or not! Ask them. Lots of places to pull over along the way to check out the scenery and watch the tide rise or fall. In the right place it is quick! The Double Muskie is a good place to eat. Mardi Gras themed!
If there isn't much interest in that, drive down to Seward for the night. We took the Resurrection Bay cruise with a stop at Fox Island for lunch. THAT was awesome! Whales, orcas, sea lions, the lunch was great with a nice calm pond by the deck to enjoy.
Do the Sea life center after if you want, or relax and explore the town. The next day drive back up and take the tunnel into Whittier to meet your uncle. Give him back his truck and when you want to leave take the train back to Anchorage. Take a cab to the airport from there. If it's way too early for your flight rent a car for the rest of the day and explore Anchorage.
Adjust your schedule as you wish but remember that drive time is not always fun time. A beautiful drive for you and the wife may be snore time for the kids.
Food stops are an entirely separate thread!