A collaboration plan is critical. Team teaching is a lot like having a relationship: who is going to do what and when. Most importantly who is going to take care of the kids, all 50 to 100 of them.
I have made animations about two kinds of collaborations styles, Ping-Pong Collaboration, where the students take what they are working on in one class to the next as the project evolves. The other video is Peanutbutter Cup Collaboration where the students do related work in different classes then they bring them together to create the whole project.
Obviously, you could do both or build another system.
After 17 years of Collaborative PBL, I know where things might fall apart and how to minimize the risks of team teaching.
For instance, I finally made sure my teaching partner did the project themselves too, seems simple but when we had breakdowns in project flow, it was because my partner and I did not know what was essential to each other planning. We are always practicing PBL.