H1B to Marriage based EAD? Employer change

Try to remain at your current place of employment for as long as possible until and after having had your I-485 approved. If not possible, then...

No need to notify NVC of anything. Simply apply for I-485 when PD current under CIS guidelines.

Cannot hold/use two identical category EADs at the same time. The issuance of the replacement one invalidated the first one.

Your only option is to wait and begin inquiries after 30 days, in 30 day intervals.

Selling in order to get rid of your old/used stuff OK; selling others' items for profit no.

I am US citizen, sponsoring parents who overstayed visa. How do I explain that they have been working unauthorized?

Better work with a competent and experienced lawyer in this case or else parents stand to be greatly disappointed.

You need to work with and strategize the "next step" with your lawyer. Nothing will happen "automatically."

I agree. Check the RFE contents and see if DNA is offered as one of the options.

Each living, breathing individual is required to complete/submit his/her own DS-160.

Upcoming merit base immigration executive order?

Pure speculation and needless "trial balloon" at this point.