This story doesn't pass the smell test in my opinion. It is incredibly hard to believe that any licensed attorney would advise these people to get a second marriage certificate and then use that certificate to apply for adjustment of status. I mean, it doesn't border on fraud, it is fraud. It just doesn't sound like something a real attorney, even a stupid attorney, would do.
This reminds me of a person who was here on an H1-B and married a US citizen. They hired an attorney to do the paperwork, just so they wouldn't have to deal with it. They filed all the appropriate documentation and only used her salary in the affidavit of support because she made enough herself. No problem. So everything goes smoothly, they get an interview date and the applicant asks his attorney what he should bring to the interview. The attorney says he should bring his wife, the originals of everything he submitted to the USCIS, and he should bring his own tax returns. The applicant says the tax returns were not asked for in the RFE and are not on the sheet provided by the USCIS. The attorney says yes, but normally the officer asks for the tax returns for the applicant even if the applicant did not use them in the affidavit of support. The applicant says, NO, it's not on the sheet, **** them, I'm not bringing it. Attorney asks, is there some problem, did you fail to file or something? Client says, no, no problem, but it doesn't ask for my tax returns, so I'm not bringing them. Attorney says, well its up to you, but I don't know what is going to happen. The day of the interview the applicant calls yelling and screaming that he received a second interview date 7 months later and that the IO was extremely rude and questioned him for quite awhile about his not bringing his own tax returns. Turns out, the applicant did have a problem with his tax returns, namely that they showed he was not working for his sponsor because his sponsor had stopped paying his salary. He was instead working elsewhere but had not transferred the H1-B. The attorney says, ok, we'll figure this out, don't worry, etc., etc. The next day the attorney gets another call from the applicant. This time the applicant sounds different, a little bit weird. The applicant starts yelling about contacting other attorneys who told him that he was supposed to bring his tax returns and why didn't the attorney tell him to bring the tax returns. When the attorney starts to talk, trying to remind the applicant that he had in fact told him to bring his tax returns, the client hangs up the phone and attorney never hears from him again. What do you think happened?
There is nothing easier than the blame game, and the OP's story smacks of the blame game. However, if I am wrong and this story is true, then these people should immediately stop talking to the attorney altogether and file a bar complaint against him or her. Advising people to commit fraud is a disbarrable offense and will be taken very seriously by the whatever state bar association to which the attorney belongs. If they paid this person any money they should sue in small claims court. And if they already filed paperwork using this second certificate, they should immediately notify the USCIS of what happened. They are going to have a lot of explaining to do, but it is going to be better than being charged with fraud.