My Little Band Pony

Twilight is the singer and helps rarity organise
Aj plays the bass
Rainbow dash plays guitar..so Aj and RBD are always having there little petty fights xD
Fluttershy plays keyboard because it's a shy like instrument like she is
Pinkie pie plays drums..I mean come on, she is that awesome she can break the fourth wall xD
Rarity is backstage (I really don't think any instrument would suit her and her voice wouldn't go to twilights) so she helps make the costumes, organise gigs (with twilights help) and sets the stage up ect. :3

All drew by me, the instruments I got of google images :3