Yes they are all needed.
You cant play the game without them
Is the guitar Instrument needed for the Guitar Hero or Rock Band games or can the Wii Remote be used in it's place? If the remote can be used, how does it work with the game?
I thought that in GH 3: Legends of rock you could use the wiimote by itself as a guitar, I may be wrong.
i think you can use an xbox controller on old guitar heros for xbox. not for wii tho.
So, if I get one of the Rock Band games and the instruments, can those same instruments also be used with the Guitar Hero games?
Last thing I know was no, but the GH instruments are RB compatible since the RB 2 in Wii