Character Development

How much should I involve my immortal characters in my book? I mean, will it just be too confusing to have these superior beings coming in? I was planning to make it so Jenny was seen as a way to getting through to Aidan, otherwise a weakness. So that implies big dark creepy people coming to kidnap/kill her. Requiring Aidan to be with her at all times for safety. Gah, sorry if all these posts seem so pointless. I just have to "practice typing" during the first 15 minutes of computer tech and typing games are such a drag. I'm just trying to pass the time. Maybe i'll just explode!!!!