You may only set one user to be an "Author" of a page. So you may only grant one particular user to be the editor of a page, other than administrators.
In this example, we have a town website that needs a user to be able to access on the Fire Department pages. You should setup a user that will be the editing user for those department pages. This user login may be shared with anyone who should have edit access to these pages (other than administrators).
1. Create your new user who will need access to edit these pages and assign them as an "Author."
a. Login to the administrator of your site (http://www.yourwebsite.com/administrator)
b. Click "Users > Mange" form the top menu.
c. Click "New" button at top of screen to create a new user. Fill in the information.
d. Click the tab "Assigned User Groups"
e. Uncheck "Registered" and check "Author."
f. Click "Save and Close button. The new user's password will be emailed to the new user automatically.
2. Assign the articles to the new author. All administrators will still have full edit access.a. Inside the administrator area, edit the article (Content > Articles > Choose your article).
b. Click the "Publishing" tab.
c. In the "Created By" area, click the user icon and choose a new user form the list that appears.
d. Click "Save and Close." The user now has edit access to that specific page. Repeat for any pages they need access to.