I feel that the Project Manager role must be given to only one person. More than one project manager will always lead to a kind of chaos. Team heads or assistant project managers roles may be given to a person who has the same capability of being a project manager. This would be better because, Project Manager is a place where a decision must be unanimously taken by a person. If more than one PM is a leadership role. Its always better to have a single leader. Too many cooks spoil the broth. There must be always one leader who must be good enough to consider all the team mates decision and make his own that will be a productive one.