A unit can only Stand & Shoot in response to one charge per turn, even if charged by multiple units. Once all charges have been declared, the inactive player can choose which charging unit to Stand & Shoot at. The unit will then Hold against the other charging units.
If a unit charged by multiple enemy units chooses to Flee, it will flee directly away from the enemy unit with the highest Unit Strength. If two enemy units have the same Unit Strength, randomly determine which the unit flees directly away from.
Note that, in its haste to flee from one charging enemy unit, a unit might flee through another enemy unit.