It means that you will be rescheduled for your oath ceremony.

What steps should we take further, knowing that we submitted several e-request to follow up on I-485 application case ?

I agree with my colleague - you may consider requesting assistance with your US Congress person.

Yes unfortunately this may happen or his biometrics may have been waived.

Yes you may request transfer to the country which you are legally residing.

Can I sponsor one of the immigrants waiting at the US border. I believe she and young child are waiting in El Paso/Juarez

Unfortunately not under current immigration laws unless immediate family.

because petitioner died the case has returned to uscis what should do to take over this case?

They may consider humanitarian reinstatement but best to consult with an attorney for guidance.

You can refer to the USCIS case processing page for specific location times.

You should submit the requested documents but if evidence or information was mistakenly not included, best to consult with an attorney for review...

NVC Case Review Time

It can take 30-90 days for review by NVC to make the documentarily qualified determination.

Yes you may apply for a second extension prior to the expiration of the initial request.