I used to watch a vhs when I was younger in which [I believe] two kids are in a music house. Every room had a different music theme... and for some reason all of the rooms had one of their magical musical instruments stolen. These kids were trying to figure out the mystery.
At the end of the video they get to a group of music boxes that come to life for them and play music and the last music box is a One Man Band who comes out with all of the stolen instruments and tries to play the kids a song and impress them but he can't play them all at once and it sounds terrible. He then confesses to stealing the instruments and says he wanted his music to sound as beautiful as everyone else's or something. This is all from memory. DRIVING ME CRAZY. Someone please help. I need the name.

I had the same problem as you this summer. I'm about 89% sure you're thinking about Wee Sing The Magical Musical Mansion. The whole thing is in segments on Youtube. Wee Sing in Sillyville is pretty good, too. :)