I am really disheartened at the snarky comments about not liking history or the outdoors. You don't know JerseyDevil's kids. The generalizations sound more like laziness to me. Kids are far more open to new things if we don't shut them out and give them a chance.
JD, why not ask them? My son LOVED both MB and OBX at that age. Neither one was crowded at all and that's in 4 visits at the same time-3rd week in April. Problem is the weather might not cooperate for doing much in the water.
Our teens loved scenic trips with hikes, whitewater rafting and horseback riding. Nantahala Outdoor Center in Bryson City, NC is a favorite among teens. https://noc.com/
It will fit in with your Plan A and it's something that their classmates are likely to never have done. You might enjoy it so much that you will want to spend the whole time there. Check AllStays.com for the cgs near Bryson City. There's several.
There's also a train trip out of Bryson City. Take plenty of photos for sharing.
This sounds GREAT. My son would have loved that. I know heading north sounds counter-intuitive that time of year but if they are history buffs there's Colonial Williamsburg in VA. Busch Gardens is open that week. Last time we were there was a number of years ago and the park needed some "love" but that may have changed. You could actually do that for a few days and Gettysburg for a few-they are less than 3 hours apart.
If you give us a few clues as to what they like, that might help.