You must submit the PCC with NVC to proceed with processing.

Personal preference by paper mail may be better.

It depends on his marital status and whether CSPA benefits him.

The USC May petition for her parent once turning 21.

Yes this could cause problems while renewing visa.

Yes you should contact USCIS to reschedule.

Yes you should answer truthfully as this should be waived based on nature of filing.

You may attempt humanitarian parole although results are uncertain.

No this should not delay the passport applications.

This shouldn’t be an issue for entry purposes.