Well, there's one problem. I don't think Ray or Egon would have children. Dispite the fact that they are way more in to their job than they are in to women,
I think carrying a nuclear accelerater on your back for years would make you sterile. Though in the case of egon and ray, that's probably a good thing, don't you think?
I'm kiddin'. You have a good idea on your hands, and it could be great if you develop it. I encorage you to push yourself to the extreme and you can write one of the best fanfics out there.
just a note for the new characters. What makes the original ghostbusters movie so great is the charisma and dialogue, and overall humor, of its central characters, so if you could make new interesting characters, you've got a new hit fan fic on your hands.