Hello Jake, welcome to Outdoors-411.
I've hiked a few bits and pieces of the AT but not the entire length through the park.
Todd has probably seen more of it than I and will chime in here before long.
All I can say is that I think your miles per day look really good for having time to enjoy the trip.
With you guys both being in your 20's you should find the itinerary you've suggested to be leisure.
I spent most of the years during my 20's in Montana's rockies. My hikes often were 25 and 30 miles during the long days summer offered. It seemed to be the thing to do at the time but looking back..idunno...
I'd read a lot of Bob Marshall's adventures
at the time and I was in the same area as he had covered so I guess I figured I'd be a lite-weight if I didn't attempt to come close to his hiking days of 35 to 40 miles.
It's good to see lots of country in a days time but there is much to be said for taking it a bit easier and having the time to see things more thoroughly.
Enjoy your trip with your brother and be sure to check back in and let us know how it goes, sharing a couple of photos with us from along the trails would be nice as well.