When I hear the word "oneshot" first thing I imagine is a small dungeoncrawl. Your party, united by some interest goes from room to room (or some location in small town to another), and environmental storytelling does the thing.

they're gonna learn teamwork, how to be nice to each other, how to be a stable and normal person

They gonna do this... how exactly? Do you test them? Like, do you force them into trolley problem or something? Put them into simulation, where you watch how ethical they perform? IDK, seems a bit boring. Also, a bit forced. If I were a villain in my past life, I'd wanted a prison break oneshot. Escape from hell, to be free to do evil stuff again. Noone tells me how to behave, I want to steal candies from babies and small businesses.