While the fact is that Xykon doesn't know how much Durkon values family (and that Durkon's one is not based on blood except for his mother) as we know, the main point against this happening is that it would be totally out of character for Xykon. Xykon has another weapon for people he really hates (and all of them are wizard and not clerics, maybe in future with the notable exception of Reddie) and it's Soul Bind. For all other living and undead being, there is fire, and sometimes lightning too.