You are the Police Officer...
You are dispatched to 123 Main Street in reference to a disturbance. Upon arrival you make contact with John Doe. John invites you inside and begins to advise that he is having an argument with his roommate Jane because she has not contributed to paying her portion of the rent for the month. While you are standing inside by the front door, you observe a small baggie of what appears to be marijuana on the coffee table and a bong in front of where John is sitting.
Based on this scenario. Do you have probable cause for an arrest? Who would you arrest? And what are the charges, if any?