You will need a conference, possibly with a counsellor in attendance. If you do not take control of the time, the remaining parents will become disgruntled. Do not let your parents stray into other areas of discussion. Your purpose is not to listen to divorce problems and so forth. Keep bringing the conversation back to the student if at all possible.
Most parents are supportive and polite.
It is naive, however, to believe that you will never face a difficult parent. If the parent becomes somewhat heated, you must do the opposite. Repeat quietly but firmly your concerns, and interpretations of the student's behaviour and work habits. Do not be intimidated or fall into the trap of losing your temper. As you remain firm and calm, the parent will eventually cool down and meet your level.