if I remember right there is an option to have an AI for one of the character but it is only for the dialogs. From a personnal point of view, I prefer controlling both of them when I play solo

"-Oh that's fullmoon, cuttie cuttie sheep
-baaaaaaOOOOORGH"
***Sprotch***

Weresheeps will rule the world (At least one night every 29 days)