Mellow

Yes you have to remove all clothing, It will be the last procedure but may be different in other countries.
Loudoff have you done your medical ? From what country ? Are you female ?

Just tell the consul at the time of interview. He/she will advise you what to do.

The parents did not get married so this is a non-issue.
ivanvash02 you have to find out exactly when the petition was approved. It is needed in computing your eligibility for CSPA.

If it's any consolation, you're not alone. I had the same circumstance as you. As of now my total wait has been 24 years, but I just get on with my life. Pursue a good career, raise good children, be a good spouse. Maybe after 20 years you wouldn't even want to live in the US anymore.

If you will not be staying in the US for 2 years why will you petition for your mom now ? What will she do in the US by herself ? Anyway USCIS requires domicile of petitioner when the time comes that your mom will prepare documents before interview. It's better to petition her after you go back to US from Germany.

If the father only wants to visit, there is a Non-immigrant waiver.
Applicants for nonimmigrant visas, such as B1/B2, H-1B, L-1, or J-1 can apply for waivers of inadmissibility, and on that ground can be granted visas or admission to the U.S. A nonimmigrant waiver is applied for at a U.S. consulate in conjunction with a nonimmigrant visa application and no specific form is required. The standard of proof for a nonimmigrant waiver is often easier easier to meet than for an immigrant waiver. The following factors are considered in granting a nonimmigrant waiver:
Risk of harm to society if the applicant is admitted.
The seriousness of the applicant’s prior immigration law, or criminal law, violations, if any.
The nature of the applicant’s reasons for wishing to enter the United States.
While a nonimmigrant waiver is easier to obtain, the drawback is that it is temporary. It is valid for a maximum five year period but only authorizes nonimmigrant admissions. It does not authorize an alien to apply for permanent residence. Only the immigrant waiver can accomplish that.

"After an alien has been removed from the United States, there are limited circumstances under which he can return. The opportunities available for returning to the U.S. will vary depending on the reason for the removal."
Your father can file for "PERMISSION TO RETURN AFTER REMOVAL/DEPORTATION". File Form I-212, Application for Permission to Reapply for Admission into the United States after Deportation or Removal. Depending on the reason for your removal, you will likely also need to submit Form I-601 which is an Application for Waiver of Grounds of Inadmissibility.
See here: http://www.vkblaw.com/law/permission.htm .
It's best to hire an immigration lawyer for this.

You can file for a late-registered marriage certificate. I don't know how you do this in your country but in ours, you go to the civil registry office and file it there.