Nick and Nate are not stupid dude. No one with a Jiu Jitsu black belt and that skilled in boxing can be considered "stupid". The guys know a lot about martial arts, conditioning, and diet.
They might not be very articulate or educated, but they are not stupid.
If you listen to their interviews, those guys often say pretty smart things and have smart ideas, they just have a hard time articulating their thoughts.
Honestly you don't know them personally so you can't exactly comment on what those guys are like personality wise. You're crazy if you think Nick and Nate are exactly the same off camera as they are on camera. There's plenty of videos of them just hanging out with their friends and they're just chill normal dudes.