Cannot see other users email campaigns in my user account

Cannot see other users email campaigns in my user account

We have two separate users for Zoho campaigns. When I log in to send an email I cannot see the other users email campaigns on my user account and nor can he see mine. I also cannot add my email address in the sender details to his and nor his to mine as it says it's a duplicate

I have changed the privaleges to full access and cannot add me as a user to the other user account as it is saying it's a duplicatation.

Paul