In my experience with Drupal, if something is difficult to implement, that usually means that you're doing it wrong. Having said that, I'm having a hard time figuring out the best way to implement a new site that I'm working on.
Essentially, the site will have content that multiple users can work on, but they shouldn't be able to work on ALL content of a certain type. One user will be a 'leader' and be able to add, edit, and remove all content related to his/her project, regardless of whether they created the content or not. At the same time, they should NOT be able to add, delete, or edit content of the same type that does not belong to their project.
Example:
Leader1 is the 'team administrator' of 'Project1'. He/she can create, delete, or edit ANY content related with Project1.
Member1, Member2, and Member3 are all associated with Project1. They can all create content related with Project1. They can also edit or delete content THEY created for Project1.
Leader2 is the 'team administrator of 'Project2'. He/she can create, delete, or edit ANY content related to Project2.