This musical medley features thirteen different instruments. One instrument is used three times, but it's easy to tell which one because someone is talking over the performance.
The guitar and ukulele were performed by me. Several snippets were taken from samples I found at archive.org; here is a list. The Irish flute was taken from here and the nose flute is from here and the ocarina is from some video game.
Then you just need to look at the first letter of each instrument's name. Yes, the answer is NOT ENOUGH PIANOS. I know that's a stupid answer. Please believe me: My hands were tied.