If you're looking to send site notifications to a member of your team that isn't assigned an admin role, an option you may consider is setting up a forwarding rule with your email provider!
Emails from Thinkific are sent from firstname.lastname@example.org or email@example.com. If you are using Email White Labelling, students will receive emails from the custom email domain you have set up with Thinkific.
An example of an email forwarding rule you can setup would be:
Site Owner receives notification from firstname.lastname@example.org with the subject "New Sign Up" > Emails matching these criteria are automatically forwarded to your team member's email address.