For the open source category, you'll need to have a README file and License file. Your screenshots are super cute so you could easily add those into your README (as shown with Mookie on stream, this is super easy to create and can essentially be autogenerated. Since Mookie was on stream with me, I did this for you all 😉).
The concept is great, fun, exciting. I like that the characters can hit multiple enemies. I enjoy the sound effects and music; they fit nicely with your game, and the sound effect for hitting multiple enemies is so satisfying. Having two "characters" to control is rather creative. Nice work. The graphics and art style is cute as.
At the end of the "level" just need a "restart" button or similar, "new game" or something (this only happened with the game was zoomed in so it wouldn't go to the next game). Would love to see more levels here too in future. The resizing might have some issues with the screen, on my first play I couldn't see the balance or slider, or enemy count, but when I refreshed and played a second time, the slider was there and the enemy kill count etc. was all visible. It was then that the game also continued after finishing a level, and continued to the next level.
I love the animation for when you change characters, the zoom out and in is very cool, nice touch. Enemies are actually really cute too. Great job on this game everyone.