for level 12, you can aim your first guy 5 squares to the left of the "l" in "level 12" and bit (only a little) below. he should fall back down to one side of the teeter totter. shoot your next man at the stone
for level 10, aim for the edge of the happy face stone (i can't remember left or right) with full power. if you can do it right, it will knock itself down, and you have to shoot it as it's falling. the most powerful is around 1-1.5 squares from the sound button
 "RagDoll Cannon"){kind=icon}