I don't see how you get 18 damage to Coralej?

First autofire is a miss for 9 damage, so that's halved 4 stun damage because autofire, doesn't exceed damage threshold so just 2 damage (stun is halved). 25/31 ->23/31
Then 9 stun damage that does hit, doesn't exceed DT. 19/31 hp. 13 stun, 6 actual.
Then it's 12 stun from the grenade, which hits the DT, and does 6 damage. For a total of 25 stun and 12 actual.

Did you not notice the first autofire was a 4 to hit maybe?

Oh and I'd like to use Negate Energy vs that grenade (1d20+14)[18] vs DC 12, and I'll use a Force Point to heal for the 12 damage it negates and saving Coralej from the condition track. Which would leave him at 31/31hp