teleporting into a besieged castle...

[tinkthank]

Wondering: Besieging an enemy Mountain Citadel, held by Ctis (Im pretty sure he's that Undead theme, forget the name, not miasma); it's taking me forever to break the defense, and although he cant recruit troops he can summon tons of these undead, and that citadel is hard to storm. +
I want to preach him out.
I have some decent mage priests who can teleport in and help in the preaching , but before I do, I am wondering:
If I teleport in, will (a) there be some funky battle with each individ teleport priest getting slaughtered individually by the huge undead army in the fort, or (b) are they ok -- they'll join my army there sieging and preaching, only to get attacked together with my whole army if they "break siege"? (Or something else?)
Thanks much