The following is the similar cases as yours cited from this website (read the red color words I highlight) and it seems you only need to pay one AOS I-864 fee for two related cases though you filed two I-864 for your parents, respectively:
http://britishexpats.com/forum/showthread.php?t=726572
Re: I-864 for each immigrating parent - questions
Thank you, Rene.
Your friend's case and ours is almost identical. Our son/petitioner also was sent only one AOS I-864 Fee Bill, but it's clearly stated that separate I-864 have to be submitted.
Allow me a couple of days to clarify some things on my part, which you then can share with your friend. It's always good to know that others are dealing or struggling with the same, and it's been very difficult for me to find someone else sponsoring both parents through Consular Processing.
Till soon again,
Connie
Re: I-864 for each immigrating parent - questions
Hi again, Rene.
Your petitioner friend is probably ahead of us in this application process, so what I am posting may be no longer of concern to her. I'll share anyway, because information on our type of cases seems to be hard to find.
1)
As I already mentioned, our petitioner son received only one AOS I-864 Fee Bill (for his father), which he has paid.
I checked on my hu*****and's AOS I-864 status on the NVC website. There is a button "Related Cases" which leads to a page stating that there was a one time charge only for the AOS I-864 due to the cases being related. Ok, this clarifies payment.
2)
Although the NVC charged only for one I-864, the petitioner needs to submit a separate I-864 for each applicant parent. They clearly state this, and it's the answer your friend got from the NVC.
HOWEVER, since the NVC billed our petitioner son only for the father's I-864, there is only one cover sheet to download for the submission of the I-864.
Since separate I-864 need to be submitted for each parent, there need to be separate cover sheets as well, as the applicant's name is typed on it (probably different bar codes as well).
I take this to mean that they will first look at/process the father's I-864. Therefore, only one I-864 can be submitted at this point.
I don't know which parent's AOS Fee Bill your petitioner friend received, but the NVC may be sending it out first for fathers based on the assumption/experience that the hu*****and is the main breadwinner of the applicant parents. If this is indeed a 2-step process at the NVC, they may be actually taking the whole picture into account and treat this case by case.
