Many Planners can coordinate on a Group Trip or Quote at the same time as Co-Planners, but only one of them can be the Owner.
Co-Planners have the same permissions via the Planner View to edit a Trip as an Owner, but only the Owner receives notifications when actions are taken on the Travel Page by Registered People.
All Team Members are Co-planners on the team trips, but Co-Planners can be added to individual trips as well. So not all Co-Planners are Team Members.
FAQ: Ready to add one, but not sure how: How do I add a Co-Planner?
The Co-Planners that are added when a Trip is created are shown in the Activity Log at the very bottom. All members of a Team are automatically added to Trips and Quotes created by any other team member.
When a Trip is copied, Co-Planners are also copied. So double check your Activity Log after creating your trip to be sure you've got the right Co-Planners.
By default only the Owner's contact information is displayed as the Contact on the Travel Page.
However (As of Release 1.50) any Co-Planner can also be:
Listed as a Contact on the Travel Page
Available as an option for sending messages from the Planner view