Distance to Davena and Garn was part of the reason I asked about the jumping, actually. Considering that there might be an actual "scream and leap" moment in the coming battle.
I love the idea of Gib taking a shot with the crossbow as an opening salvo, too. (I don't know why but I awlays forget he carries that thing.) Hold Person is also a good thought... would that keep Davena from casting, at all, or would it simply keep her still? If we can forestall her magic at the get go, that would be ideal! So, if hold person would do that trick, I vote for the spell. If not, fire off those bolts and aim for the slitch's mouth! 
Ch'dau, of course, upon seeing Kith and the state she's in, is going to be inclined to carve the widest and bloodiest path he can towards the dais. As Ara said, the objective, here, is to kill Davena as quickly as possible, so I'm thinking that taking off arms (especially where the ghouls are concerned), legs, and heads is going to be the "go to" for ol' fuzz face. Disarm, disable, and let 'em flop behind him as he presses forward. Sound reasonable to the rest or does anyone recommend a different tactic?