I use clippers, not a dremel, but there are a couple of things you can try. When you feed them, that's when to get them used to the noise. Turn it on at dinner time, bring it increasingly closer to their food bowls…...let it become a "dinner bell", so they associate the sound with good things. Let them get used to the vibration by holding it (or an electric toothbrush or vibrator) in you hand and putting your hand on the body, then a leg, then a paw, so the vibration becomes "old hat". In other words, come at it gradually so there is no "fear factor". Then, as long as there is no pain involved, you should be able to go ahead and start using it on their nails. (You might be able to desensitize the clippers the same way, but it will be harder with the boy who associates them with pain)
You should also be handling feet and examining nails on a regular basis. There should be no "don't touch my feet" reactions! If there are, you obviously need to work on that first. Reward for good behaviour, work through resistance with persistence. To me, it just isn't on to have any part of my dog's body that I can't handle.......you never know when it will be necessary because of an injury.
None of my Basenjis has ever been a fan of clippers, but it was never an optional activity. Had to be done, and was done. I don't believe in unnecessary restraint. The dog learns to be responsible for controlling himself/herself while I work on the feet. My show bitch was hilarious......she would become increasingly annoyed, then she would complain vocally, then make a slow motion grab for the hand holding the clippers. She never bit down, just registered her displeasure. I think she was disappointed at my reaction when I laughed at her.