Which NIMS structure makes cooperative multi-agency decisions?

Multiagency Coordination Group (MAC Group) makes cooperative multi-agency decisions.

MAC Group typically consists of agency administrators or executives from organizations, or their designees, that provides policy guidance to incident personnel, supports resource prioritization and allocation, and enables decision making among elected and appointed officials and senior executives in other organizations, as well as those directly responsible for incident management.

Source: https://training.fema.gov/emiweb/is/is700b/handouts/national_incident_management%20system_third%20edition_october_2017.pdf