You’re on a rollercoaster together.
Every player has one individual cart it can push up/down. (Just press your one button to jump out of line.)
Different players have to dodge/grab different obstacles/powerups, as you pull each other along the track (left to right).
Probably just have a simple “rope” equation between two consecutive players. No need to involve actual physics or difficult stuff. (So that, when you jump, the players around you smoothly go with you a bit.)
Maybe a rollercoaster doesn’t work well then, people should be loosely connected/chained in some way.