Try something like this:
Have a property in your AppDelegate called theData, and set it to a list of records like:
set my theData to {{mailBox:"Inbox", emails:{{firstName:"Ray", lastName:"Robertson"}, {firstName:"Shane", lastName:"Stanley"}}}, {mailBox:"Outbox", emails:{{firstName:"Jane", lastName:"Smith"}, {firstName:"Paula", lastName:"Ramsay"}}}}
Now add an Array Controller, call it First, and bind its Content Array to the AppDelegate, with Model Key Path of theData.
In your first table, bind the first column’s Value to First, arrangedObjects, MKP mailBox.
Now add a second Array Controller, call it Second, and bind its Content Array to First, Controller Key selection, MKP emails.
Finally, bind the Value of the first column of your second table to Second, arrangedObjects, MKP firstName. Bind the second similarly to lastName.
Now you can use the remove: method of the controllers, and you can add by modifying theData.
A tip for bindings stuff: do one at a time and test after each; it makes trouble-shooting so much easier.