How to enable site managers create Alerts and send Newsletter to their site members only?

By default, only App Manager can create alerts and newsletter.

To allow more site managers create alerts to for their site members, go to “Manage Application” > “Setup” > “Privileges”.

To allow site managers send newsletter to their members, go to "Newsletter" and add the site names to "Grant Newsletter control to Sites"

To allow site managers create alerts to their members, go to “Alerts” and add the site names under "Grant Alerts control to Sites".