By creating a group (http://blogguide.myblog.arts.ac.uk/how-to-create-a-group/) you can then email students and staff to join the group and this will give them access to the blog.
When you create the group with the blog facility you will be able to set the blog membership options (http://blogguide.myblog.arts.ac.uk/how-to-create-a-group/how-to-create-a-group-blog/)
Members will need to create an account (http://blogguide.myblog.arts.ac.uk/sample-page/setting-up-your-blog/) within myblog.arts
The membership role can then be changed for the staff within the blog dashboard (http://blogguide.myblog.arts.ac.uk/privacy-settings/users/)