How can I make posts private, but allow a higher membership level to view all?

Hi, on this site there are only a few levels. I have looked through the manual but cannot see any mention of my requirement.

The lowest level (Level 1) create posts using a form plugin (Formidable Pro), and they may view and return to edit their own posts. These users each represent different organisations, and they must not be able to view each other's posts.

The next level up (Level 2), need to be able to view all the posts made by the Level 1 users.

How can I achieve this?