Inexperience or feelings of insecurity may sometimes cause co-facilitators to debate with the lead facilitator. The best way to handle this situation is to give enough importance to them, including involvement in all steps of planning, seeking suggestions and accepting whatever is practical and/or those ideas which enhance the process. If you have a different opinion, explain the reasons and share your previous experiences in similar situations.
Encourage a less experienced co-facilitator to choose sessions that you think he/she can handle. If he/she disagrees, explain what could be the possible results and ask whether he/she would be able to deal with this. In case your co-facilitator insists on going ahead, help him/her to prepare with assurance of your cooperation. Do not invade the space of your colleague when he/she is facilitating but set up an understanding so that he/she feels free to call upon your assistance, should it be required. You should have a joint reflection after a session, not in front of participants, to find ways to improve performance and skills.