It's pretty easy actually. There three persons and each one draws one sketch, lineart, and colored picture.
Which means I would start with 1 = sketch.
Then you go down to the another row and do 2 = lineart (you'll line the sketch from one of the other person's sketch.)
Then the 3 = coloration. (You color the lineart from one of the other person's lineart)
I hope I explained it good enough... ^^'