The Mouse Guard rules are unclear on whether -- during an extended conflict, a team's actions specifically address only a single other team on each phase of the turn. I think so, but not everyone in my group agrees.
When multiple teams are involved teams should choose targets after actions have been declared.
Imagine the following three teams:
Team Saxon Team Kenzie Team Snake.
The following actions are declared:
Team Saxon Attacks Team Kenzie Feints Team Snake Maneuvers
After the actions are announced, the GM decides the Snake will target Team Kenzie with its Maneuver.
Everyone rolls dice.
Team Saxon gets 3 successes Team Kenzie gets 2 successes Team Snake gets 5 successes
Team Saxon's Attack is versus Team Snake's Maneuver. Since the Snake's roll was 5 and Team Saxon only rolled 3 successes, the Attack was unsuccessful, Snake didn't target Team Saxon so doesn't get to buy Maneuver effects against them.
Team Kenzie's Feint is Independent of Team Snake's Maneuver, so Team Kenzie's Obstacle is zero. The Feint removes 2 points from Team Snake's disposition.
Team Snake's Manuever is Independent of Team Kenzie's Feint, so Team Snake's Obstacle is zero. Team Snake has a margin of success of 5 with which to buy Maneuver effects against Team Kenzie.
These two posts cover some of this ground in detail:
The rules for Multiple Teams, Multiple Actions (pg. 114) contain this line:
If two teams have the same target and choose actions that are both versus their target's action, they must help each other rather than roll.
With that in mind, I have to assume that your action only affects one enemy team. If the action affected all enemy teams, they wouldn't need the "two teams have the same target" clause because everyone would have the same targets.
Each action you target one team, but if that team is being helped or is helping, the other team takes the effect as well.
Anyone who shares your target with a vs must help you or you them.
Further, you do not script targets; you pick and announce target when you reveal script for that volley.