If I remember correctly, you said earlier that you front loaded you application. You'll want to bring new letters of intent for each of you to the interview. Prepare a "family tree" as some couples are asked for it including a VJ member fairly recently in this forum. We provided one that included grandparents, aunts, uncles, parents, and siblings with birth and death dates, addresses, and phone numbers. When we applied (2017) and interviewed (2018) there were several VJ members in the Vietnam forum who had difficulty and received blue slips, home visits, and extended administrative processing. We corresponded with many of them and even though they had a difficult time getting their K1 or CR1 in Vietnam, everyone we talked to at that time eventually got approved.
When I attended the interview with my fiance, we brought a LOT of paper in two 6 inch, clear folders that included emails, receipts, chat logs, photos, travel itineraries, airline tickets, etc. for the time between our application and interview. I had no expectation that anyone wanted to see it. We brought that paper to give the appearance that we were ready to provide them with anything they could possibly ask for. The evening after the interview, we shredded it all at our hotel's business center. Don't bother with the translation of your chats. If they really want to read them, they have the expertise nearby to read them in Vietnamese.
I found that some of the best advice came from the HCM City consulate reviews. I can only share my experience from 2017-18, but you will get the most up-to-date advice and recommendations from these reviews -
https://www.visajourney.com/reviews/index.php?cnty=Vietnam&page=1&dfilter=5&topic=
Jason