Necroscope question

Hi, I have a question. I would like to read the Necroscope series by Brian Lumley and I've already bought two of the books in a sale (Necroscope: Defilers and Necroscope: Avengers, to be exact). I'm excited to read them but have one small issue. My question is, can I read them separately or do I have to read all the previous books in order to understand what's happening? I couldn't find anything helpful on the internet, so I hope you can help me with this. Thanks!