You can break each controller down into two by yourself. Obviously this does not work for pro controllers, but it should be no problem for joycons.
You would just map controls(0) to players one and two, with player one's movements mapped to the left control stick (subtracting 90 degrees from the stick movement) and the arrow buttons. Player two would then map to the right control stick (adding 90 degrees) and the a, b, x, y buttons.
This way you can support eight players.