This Level is much more easiër then Atreides or Harkonnen. once you start with the mission, protect the mercaneries (The Yellow Allies) by building a lot of Rocket turrets, and build a wall around their Starport, if you wait until your friend has a great force, sell the walls you build and watch how the mercaneries attack the enemy.

Note: you can also save before you let your friend go, if the force doesn't scratch your Enemy Base, Load your save game to make your group stronger, and let go again.