L.N.
Firstly, his brother is family and brothers help each other.
First (yes, I said first) this goes for you, he helped you financially when your husband was undergoing his penalty phase.
Thirdly, why are you guys going through a lawyer? They don't help the status in any way. They just file for you. If you can read and speak and write English (which you do) help out by filling out BIL's papers and go to his appointments with him if he doesn't speak English.
Regardless, this is a loan. You guys give him a loan which is to be expected to be paid back.
SIL not working- nobody's business. She has her reasons why she isn't working, just like you with one child ONLY (she has 3) needed financial help during penalty phase. Probably no one asked how come you cannot afford to provide for one child?
So do your part.
Sorry I sound harsh. I don't mean to. I know how immigration system works and I know whoever goes through that process needs all the help he/she can get.