Looking for help for the mod Blasphemous Revenants

I've got it installed, and I've made it to the necromancers hide out, I have the Soul Extract spell and the special blade, but I'm not sure how to use them. When I use the spell, it's just a self-buff and seems to do nothing - I assume you're supposed to be able to cast it on NPC's but it's a self-spell for me. I'm unable to behead corpses and thus, unable to use the mod.

I'm using openmorrowind, if that might affect it.