i'm soooo touched! thank you for putting this much efforts ; i understand why you feel stuck, too many last-minute rushes made some parts very unintuitive; and camera is a fundamental issue that needs to be resolved.
so the idea is; the big bouncy pads(what you called musical balls) that are right below the piano keys play a lullaby-like string of notes when you bounce on them - THIS IS THE SOLUTION!
for each piano key there is an option between two notes - one is right and one is wrong. so from top to bottom, you are supposed to arrange the 4 notes in the right order. how do you move each piano platform to the right node? get onto the piano platform and smash on it (E on keyboard); then you can move them back and forth using W and S!
thank you again, you have no idea how touched i am!