Scene change for a fixed amount of players

My apologies in advance, I'm fairly new to Unity.

I'm currenly developing a game with objective to serve roughly 100 players. The idea is that 100 players will be in one scene, and once they collide with one another, they both get put into a different scene. This scene will provide a "duel to the death" kind of thing, and the winner of the death-duel will be ported back into the scene with the other 98 people.

My question really is, how do I put these two players in the SAME scene? There will have to be different instances of this scene for all the different duels. How do I achieve this?

Thanks for your time reading this!