Change WordPress user roles and capabilities › Forums › Restrict or Permit access inside WordPress – how to › How to allow a user role to see and edit others posts? › Reply To: How to allow a user role to see and edit others posts?
1) role A: Edit restrictions add-on has “Own data only” option. It hides posts created by other authors from the current user at wp-admin posts list page.
2) role B: There is no criterion for edit restrictions by the role of authors. It’s possible to use tags or categories though. This post may give a starting point.