If I am not mistaken it is impossible to limit the members directory to certain member user roles.
Since this is not really an option I was thinking I would go in and adjust the SQL query myself, but first I would need to know where that is being called. Is this something you can share with me?
Members on members page shows with this query by buddypress :
https://codex.buddypress.org/developer/bp_user_query/
You can use a filter there to filter the members based on current user roles .
refer :
https://premium.wpmudev.org/forums/topic/exclude-users-from-buddypress-members-widget#post-481327