LAN only Multiplayer, Traveling Clients to another Map/Level, which aproach could be succsessfull?

Hello all.
First ill explain what i wanna do.

I want to create a LAN only Multiplayer game.
I do have the first Level, where all clients join the Server. Thats fine.
Now in this Level (its not a Lobby, its direct Gameplay) there shall be several Portals, leading to other Maps/Levels.
(I.e. the first would lead to a Level with a Big Office Building, the second would lead to a Castle and so on.)
Each Client shall be able to enter each Level alone, and some clients should enter directly without the first map into these Levels, but all shall be able to interact with each other, if they meet inside theire Levels.
We´re talking about a absolute Max of roundabout 20 Clients or less.
The First Level shall be a Gateway to the other Levels.

Now how could i do this?

I searched several Questions and answers here on the Answer Hub, but nothing i found was really helpfull.

Im thinking of 2 possibilities:

  1. Having for each level a dedicated Server, where the Clients Travel to and from.
  2. Create the Levels ( Office Building , Castle…) inside the first Level, so that the Players wont be able to see them from theire level, and all i have to do is to teleport them between these “Levels”.

Which of them should i use, what do you recommend to get my Goal reached?

This shall be a System, which supports a LARP (Live Action Role Playing) Game, so all Players are in Place, and trustable, so i dont care about cheating the System.

Thanks for all help,

Greetings