Adjustment of Status - I-485

I've filed my case on 13th april by a city lawyer which one of my friend recommended. I didnt wanted to do the lawyer at the first place but it seemed helpful that time. but i think now i am regretting my decision. Today i received a letter from USCIS regarding some missing documents in the file and it has clear warning that if fail to provide all the documents at one time than they'll deny my case.

It has asked me to provided I-864 joint sponsor's copy of green card and complete & signed most recent tax return. Now my question is my sponsor is on a green card can he sponsor me? moreover the sponsor's income was good in last year around 70k but he took some govt cash benefits like unemployment. would it be a bad effect on file if i show his tax return as a sponsor for me?

The last question is since my lawyer didnt make a good file and didnt put any effort to it. I am thinking to do all the process by myself only. Is it possible to do it now since he already prepared and sealed the document and delivered to USCIS?
Kindly please try to help me out...!!!