About a year ago I received a request to review a paper from author X in journal A. The paper uses a hype tool T to solve a common problem, which is good, but due to some shortcomings in the implementation I recommended to revise the manuscript. The editor followed my recommendation.
About a month ago I was contacted by an editor in journal B asking me to review a manuscript from unrelated authors Y. They use the same hype tool T to solve the same problem. I accepted to review it, and mentioned that I had reviewed a similar paper for a different journal (without naming it). It is now due in a couple of days.
Now to my surprise I just received a request to review a revised manuscript of author X from journal A (I thought X had given up on it since more than a year passed). I would like to accept but won't be able to deliver the review before 3-4 weeks.
This is a "winner gets it all" kind of situation. The paper that gets published first wins, and I think would be ground to drop and reject the second paper as not really novel any longer. (No plagiarism here, and nothing unethical done by the authors; just an obvious answer to an old question with hype tool T. I had myself thought of it before hearing from A, and discarded it only due to lack of time.) How should I deal with that?
Should I disclose to the respective editors that I am reviewing similar papers? I suspect that would be a breach of the confidentiality. Should I have refrained to mention to editor of journal B that I had reviewed a similar paper in the past?
Would it be a conflict of interest to review the revised manuscript from X? Should I decline the review?
Also, should I inform the editor of the other journal once the first paper gets published? If so, how can I politely ask to be informed when the manuscript gets published without giving away that there is a similar manuscript out there?