Each individual scene can only have two characters at a time, but it is possible to edit together multiple scenes to make it appear as though there are up to four characters in a location at a time.
Each scene begins with a wide establishing shot that shows that there are only one or two people in the room.
To remove this establishing shot, click the camera icon next to each scene and select “camera is skipping establishing shot”:
Add your characters and type your dialogue.
Then add the same scene, click the camera icon next to each scene and select “camera is skipping establishing shot”, and add two different characters.
When you click the play button, the camera will automatically cut from two characters in one part of the scene to two characters in another part of the same scene.