Multiplayer team selection

Hi i’m working on a multiplayer game and i’m using the “multiplayer shootout” that you can download from the learn section from unreal’s launcher.

My question is how can I make it so a big number of players can enter the server and not only 2 players, and also, how can I make a certain system that whenever
you enter the server there’s a widget which asks you if you wanna go to the blue team or the red team

My problem is that whenever someone enters the server you can only choose a player and the other someone will be with no player, as a spectator. Look in the picture below,
how do I make it so multiple players can play?

Thanks in advance