Disable Control Panel access for Coaches
If you don't want a Coach to have access to the control panel, you can control that on a coach by coach basis. Edit their coach settings to turn off access.
Disable Member Portal
This setting is under Settings -> Integrations
Disable/Enable Member Portal for select Members
As long as the Member has a valid plan/subscription that has the setting "Are People Who Buy This A Member?" set to YES, and Member Portal is enabled, they will have access.