Where it says "Sponsor's Household Size" on the HHS Poverty Guidelines, is that before or after the intending immigrant (and children) joins the sponsor?

It means now, before.

Are these immigrants family members?

They are not family members. I am sponsoring my fiancée and her daughter to immigrate with the K1 visa. The reason I am confused is that the Affidavit of Support (I-864) form is filed AFTER getting married, right? So wouldn't that mean they would be living with me at that time? It's confusing.

Are they from Nigeria or Ghana or Russia?

Have you ever met them?

They are from Peru. I have met them in person 3 times, in June, July, and October.

Have you read through this site:

Affidavit of Support Forms (I-864 series forms) - Frequently Asked Questions (http://travel.state.gov/visa/immigrants/info/info_3183.html)

They are from Peru. I have met them in person 3 times, in June, July, and October.
Good. I was worried that you have been caught in one of those romance scams.

Haha, nope. We've been talking a lot every day since early February, and I've met her daughter and parents and family, etc. I also asked her parents for permission to propose. No scam :)

I'm reading through that site now. Thank you