Assign the NPCs both an ordinary targetname to use with spawning and an NPC_targetname you can use for removal.
There are some tricks in the remove command - they were discussed in some thread a while ago. There were even some comments that originated to Raven itself. However, I can say that it has worked alright for me, at least when I have used it inside some other NPCs affect than the one to be removed. Yet, you can also use the remove("self") command. However, having no experience about that, I won't say anything more.
How is your colossal campaign coming along? So far you haven't any thread in the showcase. All this little things you keep asking make it seem as if it would soon be finished.