There are several mechanisms by which QuickBase can send emails - you didn't specify which one you are using. But if there is no customer facing way to configure the email process you are at the mercy of whatever the QuickBase backend does. In the past I arranged to send the QuickBase email to a server I controlled and had that server read the email and broadcast it to multiple recipients. You might be able to arrange this type of "email bouncing" through one of the web hook services either in QuickBase or through an external service. This is an area where features changes rapidly and people get very clever configuring it.
If you are sending the email as the result of a button / hyperlink click some of the API methods take an argument for multiple recipients and if not you could through script send two emails in succession (although this would provide less proof).
The second approach is more fun but there probably is some combination of features or services where you can bounce the email to multiple recipients. It is just an effort in discovery and experimentation.
