If I remember correctly, Divinity: Original Sin (maybe EE only) has an option at character creation to set AI controls, with different personalities to chose from, even one that agrees with you all the time to skip the RPS mini game. Esentially making one of your PCs as an NPC.
I don't know anything about D:OS2 though, but I would be surprised if they left out this option from the sequel.
That was a terrible alternative. They will either always agree with you or always disagree with you. That's not a personality, that's a brainwashed NPC that you have full control over.
