To play an eight player game in the Kung Foot Tournament mode, select the Kung Foot Tournament  painting from the main menu of the game.

Once you enter the game mode, you will see an icon in the top right corner of your screen.
 Once you press X you will see the Available Hosts screen. You can then select the host you would like to join.
 
This will allow you to play an 8 player game with 4 players per console.

You can connect only 2 Nintendo Switch Consoles together at one time.