What instrument requires two or more people to play it if such exists? I mean there is no way that one person can play it.
This article on metafilter.com lists a few:
Also: church organs before electric bellows became commonplace.
The log xylophones used in Ugandan Baganda music, amadinda and akadinda, can require two, three, or four players to play. The standard music for these instruments relies on many hands moving together to produce intricate rhythms comprised of very high numbers of beats per minute.
Here's a video of an amadinda played by six people.
Here's a percussionist who invented their own instrument; the debut performance had two people playing it simultaneously:
- Organs, before compressors.
- Bells (the large kind)
- Tooka See here
- Some Drums/Percussion
- I suppose the famous cannon
- And pipes I guess ( Think Blue man group )
Other then some drums, and really old organs, I think instruments that require two or more players are more of a "performance art" situation and not very common.