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Eleanor was just a red herring. The curse had nothing to do with her death.
Unclear if Amelia was the start of the chain (I suspect not). Maybe the reason for Rupert suddenly remembering her is the music. It does seem to hint that the piano is (almost) playing every time someone remembers a dead person.
John's suicide is unclear to me as well. Your theory about him having a mental breakdown is as good as any, but it's not very satisfying.
The hangman game has no solution. It ignores any guesses you make. Not sure what the meaning of it is. Seems pretty out of place.