Credit for this goes to
SERPENT SUICIDE as I found this in the comments section on the other solution. I thought I’d make this easier to find.
You can do this achievement with 3 controllers. Controller 1 sign in your main profile and ready up in the lobby.
Then with controller 1 again, switch profiles and sign in as a guest. It will add it as a second player to the lobby. Ready this up.
Controller 2 and 3 sign in as a guests and ready up.
You can start the game now and when you get to the level select screen, switch profiles back to your main profile with controller 1.
For speed set kills to 5. Kill the opposing colour 5 times and when the match finishes you will get the achievement.