CR1 NVC documents co-sponsor

[mveruovic 26]

Hello everyone. I’m writing to you about my cr1 visa. We’ve paid all taxes/fees and filled out ds260; I’ve also collected all documents that I need to send to NVC (I’m the applicant). What I’m unclear on is what my wife needs in terms of documents/evidence. She is a US citizen and the petitioner in our case. 
We live together abroad, and she has up until this point filed her taxes twice as an American living abroad. She has never had to pay anything to the government. Our co-sponsor is her sister (she has a house and is married, if that matters), who lives in the US and has large enough income to be able to be our sponsor. Which documents, besides form i864, do my wife and her sister need to submit?
In terms of evidence of my wife’s domicile (petitioner) even though she lives outside of the US, we have prepared her ID, voter registration, proof of home ownership, and bank account / credit card. Also, what falls under ‘Petitioner’s Civil Documents’, which is listed on the form?