US Immigration from Vietnam

Hi there! I am the USC spouse of the beneficiary, who currently has a pending AOS from K-1 visa based on marriage. We received an RFE for the I-864 since I did not make enough last year. My aunt has agreed to be our joint sponsor, and she earns over $75k per year, and has done so for many years. Steady, full time job for big corporation. However, she just turned 60 and while she does not plan to retire anytime soon, I am concerned whether USCIS will consider her future income to be uncertain given her age. I could not find much on this particular question anywhere else, so any insights would be greatly appreciated!

Just helping my wife submitted two I-130 for sister/half-sister. The first case was easy and solid since it was the same mother and father. However, the second case is little bit complicated: mother is the same, but father is different. A side note: all the parents(all 3) are passed away long time ago. For the second case, beside the birth cert that showing the same mother, what's else do we need to submit to prove the relationship?

On my wife's N-400 it says I ( USC spouse) was married two times. I was married three, two before and to her. On all other applications, I-130 and I-751 it lists all three and we have always sent in both divorce certficates. I did upload both with the N-400. Should I do something before her interview which is May 20 or just have her point out the error as soon as they start the interview? We have always sent both divorce certificates on all applications. I'm sure they will see the error.

On my wife's N-400 it says I ( USC spouse) was married two times. I was married three, two before and to her. On all other applications, I-130 and I-751 it lists all three and we have always sent in both divorce certficates. I did upload both with the N-400. Should I do something before her interview which is May 20 or just have her point out the error as soon as they start the interview? We have always sent both divorce certificates on all applications. I'm sure they will see the error.

My fiancee is Russian born and is currently living in Ho Chi Minh City, Vietnam. Her birth certificate, vaccine record, and police certificate are all in Russian. We're searching for someone who can translate/notarize these documents from Russian to English in Ho Chi Minh City.

On that same note, once a document is translated, does it then need to be notarized or is it the other way around? Do some offices offer both processes at the same time?
Any assistance is greatly appreciated.

Lastly, it appears I will need my (the petitioner) original birth certificate and copies there at the interview. Has this been the case for other petitioners who have applied at the US embassy in HCMC?