Separate affidavit of support for children?

[dm559 34]

Hi, I have a lot going on (different types of immigration) and I'm a little confused about something and I'm hoping someone can guide me a bit.

First, I'm a USC by birth.

My wife and stepdaughter is in their native country. My wife's I-130 and affidavit of support was approved. Nevada Processing is waiting for her DS-230 but we're waiting until stepdaughter's I-130 (which was approved) is transfered to NVC.

On my wife's affidavit of support is said to list anyone (children) who are going to join her at the same time or within 6 months. Which that would be my stepdaughter. So I put her name on the form. Now my stepdaughter has her own I-130 so when I submit her affidavit of support do I just send a copy of the one I sent in for my wife or do I need a new/separate one for my stepdaughter? I know it said not to list anyone who has their own I-130 (caught that part after) but nothing was said. So I would appreciate if someone could tell me if I send in a copy of my wifes or a new affidavit of support.

Next question:

My stepson is already in the US (arrived on B-2)(long story, but the original plan was for us to live abroad but after being here he really liked the American culture and how our education system is set up.) so we shifted gears to focus on immigrating my entire family (wife and kids) to US.

His I-130 was approved, did his biometrics, medical, etc. Now he's been scheduled an interview/test. Does anyone know what to expect at one of these? The only information I've found was when it was a fiance or spouse but nothing on kids. Thanks again for your opinions and guidance!