Are the children simply rebelling against their strict upbringing?
Is the boy's infatuation with the male servant a sign of possession or merely budding homosexuality?
Is the Governesses' infatuation with the master causing her to see ghostly men everywhere she turns?
One of my favorite ghost stories has been adapted and interpreted in many ways. Putting the ghosts on stage, and letting them sing, is a rsik. You reduce the ambiguity of the story. The opera still has great fun playing with who exactly can and can't see them.