Since red and green colliding is something that can only happen once in any given tick, you only need one collision check. What you're doing is finding the first event that returns true and shutting off all collision checks that follow it by using "Bump = 1"
Anyway, you need to think a bit more logically.
Do they collide?
Is the speed between the two equal?
YES - Knock them both back 50
NO - Check who is faster
Is red faster than green?
YES - Knock green back at red's speed, knock red back 50
NO - Do the opposite
Now, keep in mind that there is a bug in the platform object whereby it's speed is not constant*. It's continuously fluctuating. So when both players are running at what should be
full speed, one will almost always be going slightly faster than the other. This means that the one who is slightly faster will get the advantage. But this way the advantage will at least be random, instead of always favoring whoever gets top pick in the order of events.
*(To test this, move both of your players to the right. Keep holding down the movement keys. You can see the space between them will grown and shrink. Eventually, one may even catch up to the other.)