The chalet ghosts come with a special hidden trait that assigns them the role of the chalet ghosts. I don’t believe it’s removed when you add them to household and revive them so the game still believes they are ghosts and so can do ghostly stuff even though they are alive.
You can remove the trait with testing cheats to restore them to normal but I can’t quite remember what the hidden trait was called.
Also as mentioned the game just generates another Mimsy and Bernard if you add them to household or tamper with them. So it doesn’t corrupt your game if you do add them to household.
