Hello @Rene Francois ,
To achieve the restrictions, you should have 'Information Barriers' policies installed and configured in the organization. This can be worked through PowerShell scripts only as of now. The whole strategy can be setup through Security and Compliance PowerShell Center
Following Microsoft article will help out to give an overview and indication on where to start with.
On the other question on auditing, you need to search the audit logs under security and compliance portal as explain in the below Microsoft document