You can stop sharing email with a collaborator as long as you are an Admin of the label ( marked with a Blue 'A' on the Tandem console)
1. You need to log into Tandem
2.Select the folder you want to delete the collaborator from.
3. Click 'X' button as shown in figure below to remove this team member as a collaborator as shown in the screens below.
4 You get the following screen with 2 options
a. Delete Label ( this deletes the label from the collaborators inbox along with all the emails.
b. Stop Sharing ( this leaves the label and existing emails in the collaborators inbox, but stops any more syncing of emails)
5. Now if you select the 'Delete Label' option and Click 'Confirm'.
5. The collaborator is no longer a part of your shared circle for this label.