So I did this with 3 controllers on the online>Invite only>No AI method.
Main playing as cop.
Guest 1&2 playing as robbers.
Let the two players run into the walls and then they fall to 1hp and stay fairly close to one another ram into one after the other and the achievement is yours.
Things to be aware of It will not count if you ram a guest into the other so try and get the angle right and sort of side swipe, and they will time out so be fairly fast!
To do it legit you probably will be best doing online > invite > 7 AI and hope to be inbetween two players and them both to have fairly equal HP. Probably too much rng for me at least.