I would talk about how all three of these men are the main "rebels" in the "civilized" society. You might say that they show various levels of reaction to the values of that society.
In order of least rebellious to most rebellious, we have Bernard, Helmholtz, and John.
Bernard is clearly least rebellious in that he does not want to be exiled and he really enjoys the fame he gets from his association with John. Helmholtz is willing to really stick his neck out (poems, the brawl) and is also willing to take his exile. John hates the society so much he prefers to die.
The three show a range of rebellious reactions to the society in the novel.