Duplicate publication by the co-authors
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.