How to organise my game for multiplayer?

First of all I would like to mention that this question is not about networking and replication but instead about how to organise my blueprints in order to have multiple teams of players and how to spawn each player accordingly.

Right now I have a game with some character blueprints that represent certain archetypes such as Mage and Warrior with the appropriate logic in them. Now what I would like to do is create a Menu in UMG where people choose their team (lets say the Red team or the Blue team). Where in my game do I describe the concept of the Blue team being hostile to the Red team so that characters in the Red team can’t attack eachother but they can attack players on the Blue team?