Duplicate publication by the co-authors July 2015 : We four authors (Fabio, Alex, Haris and Mark) have submitted a paper in July 2015 and transfer of copyrights to the Journal A. Alex was corresponding author and I am Mark the 4th author. 

October 2015: The paper got accepted and published also appeared online. 

June 2016: I suddenly came to know through Google search that same article has also been published by three authors (Fabio, Haris and David) in December/January 2016 in Journal B. Fabio is corresponding author, I was not aware of this and also I am not an author in this duplicate publication. 

At the time of submission in July 2015, as per my knowledge this paper was not submitted/or being published anywhere else. 

This duplicate publication was accepted in December 2015 and appeared online on January 2016 in Journal B

In this whole situation being the 4th author in the first publication (Published in Oct 2015 in Journal A) where do I stand ? Are authors of duplicate publication guilty of plagiarism or copyrights violation ? 

What are suggestions for me ? What should I do ? Does it all effect my authorship ?
If the article is an exact duplicate

Journal B has published text which is owned by Journal A without Journal A's knowledge or permission. In that case, write to the editors of Journal A and Journal B, purely to make them aware of the situation. 

It is up to the editors of the journals to decide what steps to take. Journal B has claimed that what it has published is the original work of the three authors, and this is not true so it needs to un-deceive its readers.

Do not recommend any course of action to either editor. This kind of dispute can get nasty, complicated and damaging very quickly. And people detected in fraud (if it is fraud) will want to punish their victim. That is human nature. 

But do write. If, believing that Journal B has published a fraudulent paper, you remain silent, you become part of the fraud. 

Never accuse your co-authors of anything. Not to their face; not to the editors; not to your friends. If asked, report the facts only. Do not express judgements of those acts or those people. If asked to do so, refuse.