There is unfortunately no way to have multiple people monitoring the same user at the same time. In case you haven't tried it, you'll get an error when you try to begin monitoring with the second device. You could turn on automatic call recording, which would allow the second person to review the call later. To do so you'll need to have a Premium or Enterprise (Ultimate) account with us.
I apologize for any inconvenience this may cause.
I would suggest speaking with your Account Manager for a solution that would best suit your particular needs. We may be able to provide you a work around depending upon a few things. In the meantime, I'm going to flip this to a feature request for other members to vote on.