Since States in Wwise can only be set to global scope all player objects are affected by this stun state change. To have each individual player object affected seperately by your grenade stun effect you will want to use a "Switch" instead of a "State." Create a switch group in the game syncs tab and have two switches underneath it, stunned and not stunned, then subscribe your player switch container in the audio tab to your newly created switch group. You can then use a Set Switch event, set to game object in the scope collumn, to set your switch back and forth between stunned and not stunned per player object. I think this may solve your issue.