Are reviewers supposed to know each others' identity, after the reviewing process is finished?
No, its not normal to know who the other reviewers are if the journal has a double-blind review policy ( my background is Engineering disciplines, might be different in other fields). 

What I have experienced in the double-blind review process both as a reviewer and the author:


Knowing the other reviewers' identity during the reviewing process? NO, not normal.
Knowing the other reviewers' identity after the reviewing process? NO, not normal.
Knowing whether the editor accepted or reject the paper? NO (a very good practice as I have learned).