Here are the rules activeCollab uses when deciding who a particular user can see:
1. Administrator and people managers can see everyone.
2. Use can see everyone from his own company. If two users belong to the same company, they will be able to see each other.
3. If two users worked on a project they will be able to see each other. This goes to all users, including members and members of client company.
This is how the system is designed and this cannot be changed.
Could I also hide the list of People of Parent Company from Member?