[Faceman]

1. They are fighting because of the romance. At one point you have to decide for one of them and this will put an end to the fighting.

2. Undead in SoA are easy.
a.) There are several very powerful anti-undead weapons and items in the game that take the "un" out of "undead".
b.) To avoid level drain you can cast the priest spell "negative plane protection".
c.) "Turn undead" will easen up your fights a lot.
d.) Several priest spell are specifically designed to harm undead.