Responses
You are mistaken, "promise" happened ages ago between someone who ruled each side. He has no direct relation to that idea.
Dont overthink Minervas intentions. Until we know his identity and motives anything is possible.
Minerva is probably evil. He had the stuffed animal and he was the one that came up with the idea of splitting the world in two. Either he also eats humans that come to him from the clues (the smartest ones) or he is going to send the kids back to the farm. there's no way he's 100% good.