OK, I recreated how to do it:
First, use the CAB-2 to set up the train (lash-up) with a train link. At this point, you can toggle between the train and the train-linked caboose to trigger the TowerCom and the CrewTalk of the engine and the caboose.
Second, use a CAB-1 to set up the train following the directions on pp. 12-13 of the caboose's owner's manual (https://www.lionelsupport.com/...ents/71-9889-250.pdf). Now--with either the CAB-1 or the CAB-2--when you address the train and initiate TowerCom or CrewTalk, the engine and the caboose will talk to each other.
Cheers!
Keith