Adjustment of Status - I-485

I wrote 2 days ago about my online status which states request for initial Evidence i-485. I got it in the mail yesterday and below was stated in the request .

1. It says form i-864, affidavit of support , was submitted; however, it was not from the petitioner/sponsor. submit a completed & signed form i-864, for the petitioner/sponsor listed on form i-130. Even if a joint sponsor will be used, the petitioner/sponsor must submit form i-864. Also provide copies of the petitioner/sponsor's most recent fed income tax returns and all supporting tax doc.

Am baffled with this because, my wife who is a USC petitioned for me and her mum was our joint sponsor because she doesn't make enough income annually. We submitted my wife tax return doc( fed n state) and also my mother-in-law ( fed) last fed tax return since she was a joint sponsor...
 
Today is my day 27th and bio already done.

My question is, what are they asking for again ? Please i need this house for ideas, experiences and advice...Is this going to affect the processing period of the whole thing ?