Just make it so the cabal's inner guardian is protected from the ghost character and vice versa. Neither one can attack each other and with the changes the ghost character can't sit there and heal his friends up.

Caveat - ghosts being able to pick up disarmed weapons or loot corpses would indeed suck for the stil-living characters.

You could change the outer guardian to do this as well, unless of course it actually pleasures you to watch people accidentally slay themselves...