They suffer from delusions. Delusions about her. They think that in some way she is linked... Her soul is imprisoned in the organ pipes.
11 seconds sound clip from the Fugue in C Minor (Suspense) classic radio play.
You can hear this line at 00:07:36 in the radio play.
Quote context
[...]
- Poor beautiful Margaret. Well, it's like a nightmare, and I still can't feel reconciled, but...
- Well, what I was driving at was the children. They were in school when she died...
- I wish I could do something about it.
- It's a frightful notion, but they don't let me play when they're at home.
[...]