Hi Shashank,
Thank you for your question.The Project Manager (https://success.clarizen.com/entries/24128136-What-is-a-Project-Manager-) is only one per project. You can, however, have multiple work items Managers in your work-plan (https://success.clarizen.com/entries/24128713-What-is-a-Manager-) that are responsible for certain chunks of the project.
At the moment, you can assign only one Manager per work item, but we have a feature request on our Product Roadmap that will enable ability to assign multiple managers per work item. Please let me know if you would like me to add you as a customer requiring this feature, so that we can keep you updated on the progress. Here is ID of that feature request for your reference: CR-13158.
As for Admin privilege, Administrator is responsible for system environment settings, while Super User has “super” rights in the project management area (https://success.clarizen.com/entries/24128693-What-is-a-Super-User-). Full licensed users with Super User permissions will be able to perform all project related activities regardless of a role in the project.
All the best,
Diana