There's a way that should work, follow with me:

Step 1: Start a MP game with your buddy/buddies.
Step 2: Upon entering the game map, save it.
Step 3: Quit the MP game.
Step 4: Load the save you made in singleplayer.
Step 5: Open the console.
Step 6: Type "ai" (Without Quotation Marks)
Step 7: Save the game, again.
Step 8: Start up Multiplayer again.
Step 9: Ensure everyone rejoins the MP save as the Empire they selected
Step 10: AI should now be disabled as console changes are permanent if you save the game after adding them in.