Routing Members to only edit certain content

This seems like such a juvenile question, but I cannot find a simple way to do this.

I'm trying to edit what users can edit. For example, I would like user 'A' to be able to edit roughly 10 pages and nothing more. Those pages are in a 'parent' category. I want user 'A' to be able to add downloads, add posts, and add media but not delete anything.

I want user 'B' to be able to add, edit another specific set of pages.

Really each team-member will be editing their own department's information. I do not want them to even see the other pages in the backend of Wordpress.

Help?!