Okay, so, of the people still on their feet, Ami, Seyena, Charlotte, Raquel, Edwin, and Riven can still revive people. Well, Edwin's so far out that we don't want to recall him; he's better off lecturing people to sleep from halfway across the map. Gregor can take Charlotte's Vulnerary and get Alex on his feet, plugging that hole for another turn, and freeing Charlotte for twang-duty.
Wodan's out of range of Raquel unless Gregor moves, but if he does, she can knock 40 life off of him even without a crit. She can one-shot Paladin A, but so can Riven. That bishop's down to 7 life; Raquel can barely eke out a victory over him, unless her personal fault causes her to miss; Riven going after him puts her on the wrong side of the arcane triangle. As for Wyvern Knight B, Raquel can knock him out of the sky with a well-placed crit or with two attacks if Charlotte helps, but there's no guarantee of that, and Raquel cannot survive a single counterattack, putting the odds of a successful kill at somewhere below 50%.
So, possible course of actions that I see:
Rapid Heal: Gregor takes Charlotte's Vuln; Gregor, Ami, and Seyena heal Alex, Valor, and Tantallos. Once that's clear, Charlotte twangs Wyvern Knight B from three-range (-6 damage, if I have it wright), Raquel frotzes Bishop B, and Riven melts Paladin A. Wyvern Knight B is free to wreak havoc behind our lines, including going after our precious wagon.
All-out Offensive: Gregor takes Charlotte's Vuln and heals Alex, Ami heals Tantallos. Seyena heals Raquel, who jolts Wyvern Knight B. If Wyvern Knight B isn't critted, Charlotte twangs him (guaranteeing a kill, but check my math, please); if he goes down, she can go after the Paladin. Riven goes after the Bishop and prays. This knocks out 2-3 of the people behind our lines, but puts us at serious risk should Alex go down of even more forces pouring through our now-porous lines.
EDIT: Wait, Gregor has 6 MOV, not 5. We could have him swing at the Wyvern Knight to reduce his HP and move Ami up to heal, like scapheap suggested originally...I might need to rework that math. Err, other people's thoughts? I don't want to just propose some complex plan and order other people to move themselves around.
Gregor swings: 31-21 = 10; AS 19 vs. 14 = 2x damage. Wyvern Knight HP: 21. 34% chance of crit per attack for two attacks; 56% chance of at least one crit.
Raquel frotzes: 29-10=19. AS 21 vs. 14 = 2x damage. Wyvern Knight HP: 2. 41% chance of crit.
OK, so without healing Raquel, Gregor and Raquel together would have a 73% chance of offing Wyvern Knight B, and Charlotte would still be free to finish it off even if we fail and Raquel drops.