Your wife needs to understand that it is highly unlikely the two of you will ever be together in the USA, unless she finds a way to come and visit you for a few weeks before your interview. You have a big reverse age difference and it seems she has a health problem making it difficult for her to fly. This LOOKS to match a typical fraud scenario for Lagos, that can only be overcome with time spent together in person.
How many times have you been to see him? For how many total days? Passport stamps, are your primary evidence of being in Bangladesh with him, so you will have those, even if no boarding passes and receipts.
If her current address is not Russian (Cyrillic alphabet) then only enter her name in Cyrillic and enter Not Applicable in the first address line. If her address Belarus address is in Cyrillic, enter it n Cyrillic.
What does the actual RFE say? You've provided a lot of information irrelevant to any evidence of your intent to re-establish domicile in the USA. What have you actually submitted. What are the details of your intentions?
Yes, this is a "thing" and sometimes it works. I'm assuming your had a receipt notice for each I-130 petition to include with your I-129F filing??? As for what will happen, you can only wait and see.
Just saying that there's more to the schedule C than you described. Nevertheless, the I-864a should be provided ANYWAY. Do not wait until it is requested. That will just cause a delay.
OK. Yes, for spouse of permanent resident, you can just add the second child at NVC stage. You are all seeking F2A visas, not IR or CR visas of any number.
"IR1" is for spouse of US Citizen. Your second child will need their own I-130, just like the first child did. File it now, and ask NVC to delay both interviews until the new child's petition is approved, and passes through the NVC process.
The schedule C is how revenue minus business expenses is shown. For the self employed, "revenue" is not "income" until it appears on a tax return where business expenses are accounted for. (deducted from revenue)
Yes, in this situation provide an I-864a but I recommend it as a best practice in ALL cases.
The issue is not with NVC, but with the Consulate. If the Consulate asks for the I-864a from the joint filing spouse (at interview) then it suddenly not only IS required but the visa issue will be delayed a few weeks. It is ALWAYS the "best practice" to provide an I-864a from the joint filing spouse, whether they have income or not and whether it is needed to qualify or not.