Sorry but changing roles on a parent page does not propagate to child pages so you would have to go one by one to change the roles. When creating new pages it will inherit the roles of the parent but it doesn't get updated by updates to the parent page.
Also if you want to be able to enforce the workflow then the users should not be in a role with edit permission, they should only be in a role with draft edit permission. Users in roles with edit permissions are the approvers so they are not forced to use workflow, they could edit as draft or edit directly, whereas users who have only draft edit roles can only submit a draft.
Maybe at some point we will make it possible to check a box and push role changes down to child pages from a parent page but we do not have that feature today.
Best,
Joe