Are any of them playing dwarven spellcasters capable of casting charm? Because the "obvious solution" you've offered doesn't seem to work generically.
And of course, what are the chances that the one dwarf in your gaming group capable of casting charm manages to survive on their own, with one single low-level charmed dwarf by his side, against the onrush of all the other guards? And how does that "obvious solution" in any way alter the result of the vote?
In short: you are deluding yourself into thinking that it is easier than it is. Most players don't play vampires, because they are OP in this specific situation.
Grey Wolf