Set up 4 triggers, one for each actor you plan on spawning from (player spawn 0,1,2,3)

First trigger

Tick both -
Active on map start
Retain trigger after firing


When - an actor is clicked on by the player
Do - set single player 0 to be ai controlled
Do - set single player 1 to be player controlled

Second trigger
Untick
Active on map start
Tick
retain trigger after firing

When - an actor is clicked on by the player
Do - set single player 1 to be ai controlled
Do - set single player 2 to be player controlled

Third trigger
Untick
Active on map start
Tick
retain trigger after firing

When - an actor is clicked on by the player
Do - set single player 2 to be ai controlled
Do - set single player 3 to be player controlled

Forth trigger
Untick
Active on map start
Tick
retain trigger after firing

When - an actor is clicked on by the player
Do - set single player 3 to be ai controlled
Do - set single player 0 to be player controlled

(For some reason this last trigger doesn't change controls back to player 0)