Perhaps you'll have better luck in the scripting sub forum.
As far as the event editor goes, all instances of any given object are picked by default. Conditions only narrow down the picked list. If you have an action that applies to a sprite object without any conditions regarding that sprite, the action will apply to all instances of that sprite.
If you mean picking all/multiple sprite objects, then the way to do that via events would be adding them all (or just the ones of interest) to a family.