Advanced role management question

The Pa Legion is now moving in a direction where lay leaders will be in charge of maintaining their specific areas of the website. I am building the new page structure as follows:

Subject Area of the website parent page
-child page
-child page
-child page

I would like to create a role or custom capabilities that would allow me to assign a user to a parent page and have that user be able to edit the parent page and all sub pages.

Is there a plugin (free or commercial) that would allow me to accomplish this?