Notification email to multiple e-mailaddresses

I want to sent the notification e-mail (when someone answers) to multiple e-mailaddresses. So I made a seperated e-mailaddress with a forwarder and made all questions 'created by' the group-user.

But also for new questions I want to force this userid to be saved to the created_by field. Therefore I changed the php of several helper files, but it all results in errors. So I unchanged it all.

Can you advise me on this?
Where can I hardcode (static) the created_by value? or How can I change e-mailaddresses used to sent these e-mails?

Greetings, Rolf