Seems so. Let's see, now. A quick glance-over says that the northern choke doesn't need to be secured; in fact, by falling back, Valor and Seyena can move out of range of Sarge C or Axebloke E altogether. Key targets to eliminate are:
Bishop A: 38/38; 13 DEF; 22 RES; 51 Eva; 17 AS
Swordmaster A: 24/37; 14 DEF; 12 RES; 63 Eva; 25 AS
Sarge B: 25/42; 17 DEF; 12 RES; 43 Eva; 17 AS
Druid C: 25/35; 12 DEF; 19 RES; 36 Eva; 13 AS
Seyena can double all of these except the Swordmaster. Even ignoring her supports, her 23 RES and 23 HP makes her a decent fit against the Druid (13*2=26 damage with a Iron Lance at a guaranteed hit rate/counterattack of 17 damage at 60%) or to weaken the Bishop (57.76% chance of only 34 damage with a Glaive). Weakening the Swordmaster from a distance (59% chance of 12 damage) is also a possibility.
Valor can double only the Druid, and can be doubled by the Swordmaster should he attack from an adjacent tile. His only ranged attack is with a Francisca, which is also vulnerable to the Swordmaster's sword. I do not believe we want him moving north on his own; if he fails to one-shot the full-health Bishop to his north, that puts him out of support range of Seyena, puts him in range of three counterattacks, and threatens an overrun where the enemies can use the corridor to block us from healing him (unless we use the Rescue staff).
Olison is conveniently placed with acceptable risk to eliminate Sarge B (64% chance to hit twice with Triangle Advantage; 14*2=28 damage using a Short Spear/cannot be countered with 2 range). Druid C is an outside chance (51.84%; 18*2=36 damage using Short Spear/31
! damage at
77% chance on the counterattack), or weakening Bishop A.
Salvatore is our answer to the Swordmaster, with 26 DEF and 23 HP. Each and every single one of his Personal Skills come into play, giving him +10 Crit, +2 base damage, and +15 Hit. Even neglecting his support with Olison, attacking from range gives him a 76% chance at 19 damage, and since there's no real reason not to (2 damage max on the counterattack), using the Killer Lance increases that to 23 damage with a further 35% crit chance for the potential knock-out. With Olison just barely in support range, that's an 81% hit chance and a 45% crit chance.
And I strongly recommend that someone request that Matilda Cantos that Vulnerary out of storage in order to put someone back on their feet, if she herself is still on her feet come the next Ally Phase. ^_^
EDIT: Also, I really like Xanmyral's plan.