Any ideas on how I would make a 1 and 2 player mode game?

So I am making a game that has a 2 player mode, and a 1 player mode. 2 player mode is all done, perfectly, but on one player mode, I only want one player there, for example.

Me and my friend join the game, to unlock 2 player mode we both have to play 1 player mode. When I go to the 1st level (in 1 player mode) it is just me, and my friend gets teleported to the exact same level, but it is just him, no one else

So I guess I could make 2 copies of the exact same level, but how would I control it so only one player gets teleported there, not 2?

The max players are 2

Also this is not a request for a script to be made for me, just if someone could give me some guidance on how I could achieve this would be great,

Thanks

Sorry if this isn't a good answer, but why would you need this? Just always have it multiplayer, that is one of the whole points of ROBLOX (except for being sponsored by everything). Also I think ROBLOX can't do this, you could make other players invisible though (assuming you are on filtering enabled).