Viola

Milo plays the flute
Saike would play drums
Larry would play guitar
Nacla is a b*tch and would play electric guitar
Lay: I PLAY GRAVITY *does a backflip but floats away*

Zxi:

Lay: YEAAAAA

Zxi: HOW ARE YOU DISOBEYING PHYSYCS?

Lay: MUSICCCC

Zxi: SKREEEEEEEEEEEEEEEEEE

Zxi would most likely play the bongos,
Alan would play the cello,
And CU would most likely play a violin.

X Plays a synthboard
Tekai is a great pianist
Shai knows how to play the flute
Paladin plays the acoustic guitar

Ivan would do piano
Cakedoctor would do guitar
Madmouth would use a bass
Piekiller would use a violin
Tinior would use a flute
the rest I don't know

Astra would probably have an electronic piano

Data would have some sort of 8-bit thing like a stylophone (not sure if that's what it's called)

Terra might play the violin but I'm not sure

For collector... I have no idea.

Creatie and Tsar probably wouldn't even know what an instrument is since they're still learning about human civilization and sentient life in general

Dynamo would play the saxophone.
Byrd plays the French horn.
Setuh plays the trombone.

Potato only has a mouth so he would play the flute
Waffle only has a mouth so he would play a tuba
Peanut only has a mouth so he would play the drums with his head
Autumn would play the violin

Rizu: Violin
Rea: Grass Whistle
Cataclysma: Harp or classical guitar
Kenshin: percussion instruments
IP: surprisingly anything death metal
Pearlfan: E

electric guitar or bass guitar