We were trying to play as 4 players with the following setting : 2 players in local with 2 steam controllers + 2 other players in another local with 2 steam controllers. It is doable as we managed to make it work after nearly 1 hour of struggling with the "add local player" option.

This option is totally broken, what we finally did to make it work is smash the buttons from keyboard (Return) and both controllers (A), until the player was finally created. Sometimes, the same controller controls both, sometimes none can control it. It seems totally random and absurd.

Honestly, this does not seem that hard to fix and it is a HUGE problem for the game. I was considering investing some more into this game as it is incredibly fun but if it takes 1 hour to set a game, I'll give up soon...