Im just gonna post this as a new made forum for people like me who know what triggers are, but who have trouble with certain functions or people that just like discussing the triggers associated with making the perfect RPG maps.

How do I set an Active computer player to fight with the other enemy computer while one is one your team??

Set alliance status in the computer's triggers. Both computers should be enemy to the other.
You always modify the alliance status of the player that runs the trigger action.
-> Computer's trigger: always -> set other computer to enemy, set human player to allied

Do the same with the other computer (except the human's alliance).

You should ask this in the map making assistance forum!
This place is for people who are currently making a map and want to present their result to gain feedback.