According to the American Association of Colleges of Podiatric Medicine, a Doctor of Podiatric Medicine (DPM) is a medical specialist who diagnoses and treats conditions affecting the foot, ankle, and structures of the leg.
The NVC is a Department of State (DOS) facility that handles immigrant visa-processing. liaison between USCIS, the green card applicant(s) and the consular post abroad. After USCIS approves your immigrant petition (I-130 or I-140), USCIS will submit your approval to NVC.
Of course, that's the first stage of the process anyway. If your parents are back in their home country, once approved the petitions would go to the National Visa Center, which would contact you and ask for addiitonal information. Usually, processing at the NVC takes several more months.