Yes, more facts are needed in your parent's case. Consult with an immigration attorney.

This offense is clearly within the statutory period. Therefore, your application will be denied due to lack of good moral character. Consult with...

Contact the German embassy. It is the responsibility Germany to inform on how persons maintain German citizenship, not US.

Contact the embassy of that country. Whether or not you get their passport is up to them and not the US.

I recommend an info pass at the Field Office. The information officer will update you on the I-485.

In general, a single DUI conviction is not per se disqualifying. Expungement of criminal record has NO EFFECT on immigration matters.

Yes, you require an application for your wife.

If you have doubts about the two opinions, retain an experienced immigration attorney to advise you.

It is difficult to find an attorney on very short notice. Do your best to find one. Good luck.

You are right on not following the advice of immigrant acquaintances. Consult with an immigration attorney instead for your options.