My oldest is 6 and second child is 3. Going with toddlers is very different from going with little kids. It all depends on gender and what the child enjoys.
HS & AK were our favorite when DS was younger. Both my kids loved the Disney Jr show, playground, and Toy Story Mania at HS. We watched some of the shows, DS doesn't care for the Beauty & the Beast but my DD has always loved them, even as an infant. (My fav Baby Center is HS!) At AK we watched all the different shows, petting zoo, animal trails. Once DS was tall enough for some of the rides at MK, we have been mostly MK. DD tags along because she's fine just meeting the princesses.
For split stays, it helps if your nappers can nap in the stroller. And that you are ok with a full day at the park on move day. We have done ok with 1n at the beginning of a trip to test out a resort. If we have a 7+ night trip, I would be fine splitting it 3 and 4n. If you're pushing a double stroller, I would consider a split between BLT and an EPCOT resort. 1 or 2 days at MK, 1 full day at DH, then skip AK and Epcot for pool time.
What we've realized with our kids is that the longer the trip, the more grouchy they get

Even when we cut back park hours (say a few hours before lunch then back to the resort). By the day 5, they are just tired. Instead of popping up at 6am, we can't even get them up at 8 for a breakfast reservation. And the lack of healthy food choices (that my picky eaters will eat) doesn't help. We've gone from week long trips twice a year to multiple 4-5n trips a year.
Good luck. Enjoy and don't stress to much.