To achieve this functionality you need to build Access group -> Access Role and define appropriate Privileges and Access When rules on your work class. This will control visibility and read only access to your work object.
You always have work group and its manager to control/oversee work of their subordinate.
B and C belongs to work group RED and its work group manager will be A.So User A will able to oversee work of B and C
E and F belongs to work group BLUE and its work group manager will be D. So User D will be able to oversee work of B and C