Question:  Is it possible to add other team member as "CC" to esignature request?

Answer: Sure, please update and customise "Gear wheel > Settings > Emails

This is available for all "Outgoing Mail Server"

add the email address - 

Other way-

Set up "Email Settings". If you are using your own mail server (gmail/microsoft) you can create your own rules (ie auto email forward, email copy for your team member). You will add the rule directly to your email settings.

Note: They only received the copy of the tax return, but unable to sign it.

Also, you may set-up Settings > Esign