If you listen to - https://www.youtube.com/watch?v=i7b8JIOPEUk (0:57) and - https://www.youtube.com/watch?v=TGO72jL7veU (0:22) and (although I think I made my point) - https://www.youtube.com/watch?v=1GUWJ-B7eYw (0:8) you hear an instrument that, to me, sounds kinda like a theremin and some wacky hammond organ mixed together. Does anyone know what this is called? Thanks in advance.
That is indeed an organ. Maybe barrel orgen which imitates an pipe organ. This info is not that specific because barrel organs imitate a whole orchestra, so the sound range of barrel organs is quite wide and divers.
The suggestion of a barrel organ / pipe organ fits the historical dark cabaret / circus waltz setting and similar usage of a organ like in the Haunted House piece underlines the spooky vibe.
I needed to research that too and found your question on the way. Thought you want to know what I found.