That's the whole problem, I did have 2 X-Box controllers plugged in and I could only choose bodyparts on them. Ingame keyboard moved both players :/
I belive we could describe this better, in-game. When game starts every button on your controller (A,B,X,Y) are used to control each limb of the monster. In-game keyboard was a debug feature that I should remove before sending the final build :/ Also if you have more than two different controllers connected to your computer, try to disconnect other gamepads.