need help pls - F4

[mikky sudjadi]

- inception date of my F4 application has become current, petitioner is my USC brother
- have paid all necessary fees
- however, he has problem w/ his W2 and financial docs, and refused to send them

can i substitute my brother to my sister as petitioner ?
she is also a USC thru' marriage
if yes, however, she's only working part-time, doesn't meet financial requirement
can she joint sponsor for affidavit of support w/ her husband ? he's willing to help

i thank you