Common subgroups for different projects

Use case:

I have that may or may not have the same leads working on a daily basis so I can categorize each project into 3 subgroups: core (full access members), internal followers, external collaborators

Sometimes, we have internal followers who can be the same group of people for multiple projects.

External collaborators will always have Limited access and visibility into ONLY certain folders.  Members in subgroups are likely mutually exclusive but could overlap.  If overlapped, highest access level is taken recursively.

Say I have Project 1 with the following subgroups (sg):

sg1_core, sg1_int-follower, sg1_ext

Proj2:

sg2_core, sg1_int-follower, sg1_ext

Currently, I don't have a way to share sg1_int-follower with both projects.  I do not wish to create multiple group names with the same members.  Hence, tagging should be allowed to reference any group under parent groups.

2) when assigning folder permissions to these parent groups, it would be nice to have a changeable permissions tree open up allowing change to parent level and below. i.e. say I share a certain folder with group Proj1 with full access but wanted to sg1_int-follower to have limited access, I should be able to do this in one shot.  The current alternative to accomplishing this is to add sg1_core and sg1_int-follower separately and then vary the permissions differently.  This is obviously more cumbersome!

User also don't know which groups are subgroups without having to flip into the 'accounts' page to verify who and which subgroups are part of the parent group they are selecting.