You triggered another thought: Arrange the croup in a slight semicircle, centered on the camera lens. The goal here is to try and achieve a constant distance from the speedlights to the subjects, for uniform illumination. In my friend's image, this was not possible due to the size of the group, and a slight underexposure can be seen at the right and left edges of his image, and some fall-off front to rear.
This may not be necessary with the arrangement you suggest, but something to consider if Joanne is faced with a more difficult setup and composition challenge.
"Guerilla Group Shooter" ... It has a nice ring to it.
HBB in Phoenix, Arizona Nikonian Team Member
Photography is a journey with no conceivable destination.