[Multisite Privacy] Manage access rights per branches of pages

We are currently moving the content of our websites (hosted on a different CMS) to WordPress instances. We have currently 300 websites we\'d like to consolidate into a couple of WordPress instances. Part of those 300 sites are intranet sites.

Unfortunately, WordPress does not allow to manage access rights \'per branches\' of pages.

We\'d like to manage access to WordPress pages and sub-pages:

by branch
by group
The idea is to have access rights very similar to NTFS file system rights.

We have found a couple of plugins able to manage rights (such as \'Restrict User Access\') or articles describing how to create custom roles, add tags to a page and restrict access based on the roles and the tags, but nothing having the concept of inheritance.

Does someone know a plugin that would allow us to do that?