Help for I-864

[AnythingButCommon 2]

Hi,

I filed My AOS before one month and I got the letter for REF document that I am not meeting the Poverty line requirement.

Now, My father in law is working and they were 4 family member. Now My spouse living with me so Now they are 3 family member. My father in law , Mother in law and brother in law.

my mother in law not working any more but she used to work before December,2010. My father in law is working. They filed the join tax return for 2010 and their income was about $57,000 .

Can any one tell me that I have to file just one I-864 or two I-864 for both my father in law and mother in law?

And If I have to file two I-864 they Can my mother in law be joint sponsor even she is not working?

Please Please help me .