How can they operate this, they are a horse!
I can only see four instruments, a banjo, an accordion, a horn, and a harmonica. The horn and harmonica appear to be played in an alternating fashion one after another, the horn wrapped around her body and the harmonica probably attached to the horn. The accordion is being played via her up and down motion. The banjo just lays there in front of her around her neck and isn't being played as far as I can see. I can also see a tambourine taking a closer look, and it's being played in the same way the accordion is. Her legs show brown straps which is probably a part of something that holds everything together.
lol look at me trying to make sense of a cartoon.
also how do they hold a hammer to build their puke looking city, Equestria.
Unicorns used their magic, obviously.