How to send FYI notification to all direct reports in Document of Records Approval rule?

Summary:

We have a requirement to send a FYI notification to direct reports (subordinates of given manager or employees under manager), when giving an acting assignment (a delegation of a manager position given to one of employee or direct reports for certain period of time). These Acting Assignment is created using document of records. We are able to achieve 2nd level Manager FYI. But one major challenge we faced is notifying other direct reports (subordinates) to be informed about the new manager (delegator). Any help can be appreciated. Note that we are not using position or job hierarchy in