My brother just got married, he wants to file for his green card, he had a baby from a one night stand, he was taken to court for child support, but because of him being unductumented, he can't really find a job that pays well enough to pay his child support, how would this affect him in filling his paperwork?

Hold the green card issue for a while... he needs to get the child support order in place first. It doesn't matter how much he makes, child support is calculate based on his income.. he must pay. No excuse...

Owing child support could cause him a fortune, not just green card... it can't be wiped out under chapter 7, and the record will haunt him for life. Contact Child Support Services and get things in place...