The phrase "are cahoots with" means to be in a secret partnership with someone for a dishonest or illegal purpose. The antonyms for this phrase would be honest, transparent, above-board or trustworthy. When you are not in cahoots with someone, you are being open and honest about your actions, motives, and intentions. Alternatively, you might choose to "turn against" or "expose" those who are in cahoots, thereby removing them from their illicit activities. Overall, having an honest and ethical approach to your dealings with others is the best way to ensure a positive outcome, and not slip into the murky world of cahoots.