I mean, yeah makes sense that the doubtful one and the salesman wouldn't want to actually go and try to kill the demon lord, when their only future is to get put inside an abomination to continue torturing an already oppressed race.
Much less when, should they try and go ahead with it, they're most likely expediting their death at that point. The adventurer certainly is doubtful, but so long as someone capable is paying attention there shouldn't be much issue if he tries to stab them in the back later on.