Thank you for the reply.  We are able to create and edit templates fine.  The templates are generic and we need to change the email to add specific information for the client receiving the invoice.  Maybe the information I found in the 2nd link you provided will help explain.

Email attached documents

If you want to share a file, you can add attachments to your email.

1. Open the transaction or record with the attachment.
2. Select the Attachments icon. The attachments window appears.
3. Select the file you want to email.
4. Select the Share icon.
5. Select Mail. QuickBooks creates a draft email message using your default mail client.
6. Edit the email message, then select Send.

Step 6 is edit the email message and Send.  We do that, but as soon as we hit send, the changes/additions we made to the template are removed and the client only receives the generic email without any edits that we made to the message.  Again, this happens to only 2 out of 9 users, so I'm sure it's a setting that I can't find.