You can do 2 by default by starting it as a two player game. 4 will probably need the workaround.
Oh, I forgot the game has couch co-op.
Will that mean we can start a 4 Tav playthrough with only two instances of the game running?
That would be awesome. Running 4 instances occasionally caused issues. Nothing like building 4 characters only to have the game go “nope” and give up.