Not sure why anyone would move their unit into such a situation, but if you had 3 units with Standby and a unit moved into range 2, would all three be able to trigger their Standby? So all three units could attack off the same trigger? The Standby listing in the RRG doesn’t say anything about this.
Is there anything about timing that would prevent this? So if you get the first Standby attack, the trigger has been interrupted so you can’t have a second, or third cause the trigger was spent? There are several rules that elude to that fact, but nothing concrete that I can remember.