I don't recall what Nick said about the school teacher. Was that his "Puritanically Scandinavians" comment?
On one hand, I think the Rekietas groomed them into this. Always on the prowl for more couples to hook up with. On the other hand, Aaron cheated on his previous wife and was totally up for this, proving that Aaron hasn't functionally changed much since he cheated on his last wife. And as man of the house he should have nipped this bullshit in the bud instead of diving in head first.
And on the final hand, they are ALL fucking adults who could decide who to fuck or not fuck. No one forced anyone to do anything. Nobody shoved the cocaine up April's nose. Nobody forced the molly down her gullet.
Any one of these adults could have put their foot down and had the totally sane gut instinctive reaction that this was a ruinous bad idea. And buy putting your foot down, they could have dragged their own partner away from this bullshit, or divorced them for destroying their marriage.