Nestor:
Check the game map...the Amazons are the red dots in the trees. Cuivi is the blue dot in the tree. The Heart of Oak is near the mouth of Phasis but I forgot to put it on the map.
Wow, I never knew we had a game map before!
Well, the casting time for Leomund's Secure Shelter is 4 turns, and besides we're probably going to need that to sleep in at night, so I'll hold off on that.
Balthazar casts Monster Summoning I - elves again would be nice. I assume that his invisibility isn't dispelled until he actually orders the summoned monsters to attack. For the spot in which the summoned monsters appear, he chooses the swath of forest directly northwest from the center point of the Amazons. That way, they'll come into being able to take cover from the get-go, and what's more they may be able to get rear attacks if all the Amazons are focused on watching the south. At the very least it will turn them all around so that the party can then advance. Balthazar is hovering 3" above the spot where the summoned monsters appear. Just after he orders them to the attack, he casts sleep on the amazons, targeting those a bit farther away that wouldn't immediately be the subject of the summoned monster's initial attacks.
Between the summoned monsters, the sleep spell, and Amazons wasting bow shots on targeting the hovering Balthazar who is protected from their missiles (assuming none are magical) this fight should be under control. If need be, Balthazar will follow up with magic missile and stinking cloud as appropriate.