Taxing 12 is improved to 2 builders using the ceiling route. The Tame 20 glitch is used to get a lemming up there, and he can later dig a tunnel for the others to climb up.
As for Taxing 13, I'm going to go ahead and suggest 1 climber, 1 builder, 2 bashers, and 3 miners as a starting point. There may still be room for improvement, but so far I haven't had any luck.