To send a mailing to all clients and track who was sent the invitation and who responded, you should use Campaigns in NPSP. Here's how to set it up:
Create a Campaign:
Navigate to the Campaigns tab.
Click "New Campaign" and fill out the necessary details such as Campaign Name (e.g., "Workforce Development Program Invite").
Filter List View for Clients:
Go to the Contacts tab.
Create a new list view or filter an existing one to include only clients. This might include adding filters for criteria that identify clients, such as specific Account Record Types or custom fields.
Add Contacts to Campaign:
Select all the clients in the list view.
Use the "Add to Campaign" button to add these Contacts to the previously created Campaign.
Track Responses:
After sending the invitations, track responses by updating the Campaign Member Status. This can be done manually or through an automated process if you have integrated email tracking.
Create a Campaign Report:
Go to the Reports tab.
Create a new report using the "Campaigns with Campaign Members" report type.
Filter the report to show the specific Campaign and the statuses of the Campaign Members (e.g., "Sent", "Responded").
This process ensures that the nonprofit can track who the invitations were sent to and who has responded, providing a clear view of the engagement for the workforce development program.
Reference:
"Campaign Management in NPSP" from Salesforce Help: Campaign Management
"Creating and Managing Campaigns" from Salesforce.org: Campaigns Guide

https://www.plative.com/preparing-for-salesforce-data-migration-with-nonprofit-success-pack/

(Role hierarchy)
https://trailhead.salesforce.com/en/content/learn/modules/data_security/data_security_records Role hierarchies ensure managers have access to the same records as their subordinates. Each role in the hierarchy represents a level of data access that a user or group of users needs.