Units in ManageBac are designed to be planned collaboratively. Multiple teachers can be added as unit authors via the Add Author button in the unit planner.
MYP and DP:
The dropdown will show a list of the teachers of the class. Before teachers can be added as unit authors, they must first be added as teachers of the class. You can add a teacher to a MYP or DP class via Overview > Edit Class Settings > Teachers > Add New Teacher.
You can add a teacher to a PYP class via Inquiry > Class > Add Teacher.