Hi, sadly it's not possible to play at less than 4 people for now. We took this harsh decision with this thought in mind as we wanted to focus on the "optimal way" to play Herberus rather than on its accessibility.
There are a few tricks that allow you to complete some parts of the game at 2 or 3 if you're really well organised but you probably won't be able to leave the menu scene that easily. All the characters need to be in a elevator to leave it (we might update this during the next days).
Grab a few friends and go ! :)
(Herberus is compatible with dualshocks as well)