Either narrow the permissions to just the BU or Parent-CHild BU if the problem is they are seeing things they must not be allowed to. If it is just for convenience that they want to narrow things down, then use a view such as one of these patterns:
(thing) > Owning User: Manager equals current user (eg "my direct reports' tasks")
(thing) > Owning User > Team: Administrator equals (eg "my Team members' phone calls")
(thing) > Owning User > Team > User member equals current user (eg "My team-mates' appointments")
(thing) > Owning User > Business Unit > Parent Business Unit > User member equals current user - eg things owned by anyone in any child BU of my BU (but not in my BU)