Resticting visibility users in direct messages

I am trying figure out, how to hide for some users other users in direct messages.
We have managmet users, which should will be not visible for sales representants. Sales representans shoud be able send message just to their team leaders. Sales representants should not be also visible for eachother.
I am able to handle this?
Thank you

Not sure if this would be a good idea, but technically it might work to use lots of separate Teams for this purpose:

Configure MM such that only users in the same Team can message each other, and the create a Team for each Sales Representant and also add his/her Superior(s) to that Team.

In this case, the Sales Representant will only see her/his Superior(s) in the list of users.

Not sure how this scales up with that many Teams (depending on your number of Sales Representants), though.