Howdy Nicole!
I'm so excited for you!! What a magical trip this will be for you and your girls!!
Both resorts are amazing but I am inclined to recommend
Disney's Caribbean Beach Resort.
I believe your bus trip might be a bit shorter but more importantly, I think Caribbean Beach would be well suited for nap time.
The resort is built around 45-acre Barefoot Bay and is divided into 6 villages. It's a very large resort. When we stayed there, we loved it. It was a beautiful resort and our village was very quiet. Great for taking naps or going to bed early with little ones who desperately needed their beauty sleep.
Regardless of the resort you select, when you make your reservation, you might mention that you would like to be in a quiet part of the resort so there is less likelihood that your girls will be interrupted while they sleep. It may mean walking a bit farther from the bus stop but you will enjoy the opportunity for a little rest and relaxation from time to time during your visit.
When my kiddos were the ages of yours, there were a few times that we stayed in the theme parks while they napped.
At Magic Kingdom, there is a great spot over by The Hall of Presidents. We would grab a funnel cake from Sleepy Hollow and enjoy a snack while our kiddos rested. It was wonderful on those days we didn't want to head back to our resort.
Thanks so much for your question and please let me know if you need any further information as you plan your vacation. Have a magical day!