François + Daphné
I'm not really sure I understand what the bit in italics actually is getting at. I don't really see that it would make a big difference if a ghost master (the ghost player) said "Oh no! you've just caught one of my ghosts!". The hunters still don't know what other ghost that player is controlling.
If the hunters know that a ghost master only has one ghost left, they will know that each destruction comes from the same room; if the hunters do not know which of the two ghost masters still has two ghosts, they need to assume that the destruction can come from two distinct rooms.