I don't think there is a problem with them co-existing. It could very well be possible for a spirit to be in some sort of a limbo -like or purgatory like state before reaching it's final destination.
We hear all the time about loved ones visiting those they left behind, or being seen by them around the time of death, etc. Who's to say they didn't remain here for a while for a reason, before going to heaven?
I guess we won't know the answer, and those who will, won't be able to tell us. It all boils down to faith, and belief. I believe. I have faith. Therefore, they can co-exist.
I really don;t know how to say what I think. It's hard to put into words, but this was the gist of it.