The ally class and enemy class should fight each other when they meet. To get them to meet from distant locations, you'd want to use a control zones. Create control zones, assign whichever AI to those control zones, and the AI will move from their placed positions to those zones. There are youtube videos that cover control zones. You can also use this method to make AI drive vehicles ~
You can not do that, enemy AI will not be violent towards their own.
Only thing you can try is fake this by having the AI shoot at an animal or allied NPC that you hide behind a rock or something. The player won't see it, and from their perspective it may look like enemies are engaging eachother.
But they won't fight to the death.