The easiest way to do it would be to create a family and put only the player sprites in it. That way you can pick two seperate instances independently. A side annoyance is you won't be able to access the instance variables from the family unless you recreate them as family variables, change over the events and remove the old ones.
So for example if you called the family "other" then your events could look like this:
Fighter: control = -1
Other: control = 0
Fighter: X < other.x
--- fighter: simulate left pressed
Another way to do it without a family would be to pick one fighter, save it's values to variables then pick the other fighters and compare with the variables. It's doable but is tedious.