First things first, this is going to be Alien II all over again, so prep for your group to be the Ripley's. It's an insalvable situation unless you can use heavy Exalted cheese.

Second, d'you have summon spells? They'll be vital in battle.

Third, if you wanna get some use from the person with high INT and a +1 rapier, I THINK warmage used INT. If it doesn't, search for a batsorc like class, rapido!

Fourth,, if you can cast "greater/normal magic weapon", now is the time to use it and give a few super arrows to the archers.

But mostly, prepare for going down, wether in a blaze of glory or obscurity. This ISN'T going to end well.

PS: Actually, it might end well. Find a way to guide the zombhus against the Kythons. Weaker Kythons and less zombies is good.