Form I-130

I applied I-130 for my father to get his GC through Consular processing. I'm a US citizen myself. However I got RFE asking for his birth certificate. I have these queries:
The supplemental documents for I-130 for parents as per USCIS application only need US citizen's birth certificate and not the parent's birth certificate. So I don't understand why RFE was issued at this stage?
My father was born in the time when the birth certificates were not available. As per the dept of state reciprocity website, it clearly states:
"Exceptions: Birth certificates are not available to persons born prior to 1968. "
Since it is acknowledged by reciprocity that birth certificates are not available, do I still need to provide NABC (Non-Availability of Birth Certificate)?

I have a question regarding the impact of the recent Executive Order on my parents' greencard application, which is currently underway. I’m a US citizen (India-born, recvd greencard via EB category) and have sponsored the greencard application for my parents, who live in India, via consular processing. I-130 is approved, and we filed DS-260 and Form I-864 on 4/22 before EO was announced. Does the EO impact their case, or given it’s already in-progress (past I-130 approval), will it continue unaffected?

I am planning to sponsor Visitor Visa for my sister,she was diagnosed with Down syndrome when she was 1 year and she is now 45 yrs old.
Considering her condition, i would like to know what additional documentation is required for visitor Visa B1/B2 apart from I130, letters to consulate & bank statements.

I would like to know whether I should update my residential address to USCIS or immigration department in order to keep them informed of my updated address?? Since I'm the beneficiary and my wife is GC holder, she has applied for my I-130 of family based Green card when I was in New York and now I've moved to South Carolina, are we suppose to inform immigration department? If Yes who should inform them, can I give a permanent Mailing address different from my residential address since I may be working on short-term contracts.

I would like to apply for green card for my mother and father. am a US citizen, they will be coming to US in next month on tourist visa. How long will I have to wait (day/months) after they land in US, before I can file for their green card.? Also, if law changes for so called "chain migration", can that law be retroactive for applications in the que? Any comments on that would be appreciated.