Bill and Juliana

The answer is no, you can't claim another birth country because it would be fraud and you are looking for a way to cheat the system.
The wait is long for a reason. Don't take this the wrong way but in the eyes of the government you are not high priority. To US immigration you are an adult and can continue with your own life. There are USCs and LPRs who have spouses and minor children who are in another country and need to be reunited with them faster than you.
Again, this is not meant to put you down, it is how immigration works.
You are fortunate to be able to visit during your immigration process.

Your attorney is advising you to break like a minimum of 5 laws, dude.
And some of those have serious consequences.

This is why I was asking. Didnt sound right.

I'm not interested in doing anything illegal. Just wanted answers. These are the things my attorney told me.

This attorney of yours is shady to say the least.

Your fiancee has a full house, so that complicates things to make this "as fast as possible". I suggest you post about the divorce issue on the Ireland forum for better answers.
Regarding visa shopping, overstays, AOS through visas other than K1... nobody here will advice on the best way to commit fraud.
Mods should close or lock this thread.

Don't the children need to go to school?
I would look for a better lawyer.

K1 (fiance visa) requires you both to be free to marry, she isn't.
CR1 (spouse visa) requires you to be married, she can't marry.
Everything your lawyer is suggesting is fraud or shady grey area. Find a better lawyer, maybe one in Ireland who can help with the divorce? Without that, not sure how you're going to get this done.