Hi Syam.

More info.
If I set person A up – their account along with any account will have the primary role via wordpress as Subscriber. (The minimum permissions)

Via your role plugin, I can then create a group for managers.
If I allow the managers roles under ‘users’, tick the following:
list_users
create_users
promote_users

The person in the role can change the primary role of the user, example make them an administrator etc.
It would be good if the primary role via WP could be locked down, I can’t specifically see away to do such. With the primary WP role locked down this could then allow the roles only to be changed with the promote_users ticked under the role.

Hope that helps give some more info.
Will submit this and then send my email via PR.