Yes, Theryndil has no penalty to fire into this melee.
Amanu, don't sell yourself short. I think you have added a lot to the story, and the cyborg abilities have come in in interesting ways.
Theryndil's arrow hits the body of the creature (5 damage). Leopard fires two arrows from the other side, this time hitting one of the undamaged heads (7 damage).
Erenal executes a flurry of blows against the creature's body, failing to stun it but having an effect (17 damage). Amanu's spell also tears into the hydra's skin (15 damage).
Arramor casts cure serious wounds on Marcus, completely healing his squadmate. Reinvigorated, Marcus takes out one, and then another head with Cramp (15 damage twice).
The hydra changes tactics. This time several of the heads breathe an acidic cone which covers its three attackers. Marcus avoids the worst of the gas (8 damage), but Arramor and Erenal are hurt badly (17 damage each). Huge wings also unfold from its back, and it begins lifting off from the ground.
I should say, since neither of them are here, that Erenal is at 1 hp and Arramor is at 4.