It isn't possible to receive replies back to multiple email addresses when sending an Email to SMS campaign.
You can receive replies back to either:
Your account email address
The email address that sent the Email to SMS
By entering a custom email address
Alternatively, you can set up an email distribution list on your mail server, and then have the replies sent to this distribution list.
Or you can configure email rules to auto-forward the incoming SMS to specific emails to achieve this as a workaround.
Please see the article on setting up Email to SMS. To manage where you would like to receive replies, please see the article on Can people reply back to my Email to SMS? (Two-way communication).