Hey, derpy! I'm obviously not the creator, so this is just how I chose to play it. Your successes block damage from all enemies, and when you take damage you take from all enemies as well.
With your 5 successes, you blocked all damage that round. If you had only 3 successes, you would have taken 2 damage (1 from each enemy).
I'm not sure if this breaks the balance too much, but it worked for me.
Let's see if Roll responds!