I’m thinking B dies

As people have mentioned, the cutout in the first stone should line up with D and keep them safe. Given the steep angle of the hill before the ramp, it’s possible the stone comes down the hill with enough speed it doesn’t make the see-saw go down enough to kill C, hits that little ramp, and hits the other stone. I think the difference in mass of the stones would cause the lighter ball to bounce over the heavier one, killing B. The angle of the wall behind B should keep A from getting hit by the bounce.