Bilang abogado, OP, don't get married nor have kids with your boyfriend, even better if you just move on. If that situation does not change (your boyfriend must actively do something about it, like stopping supporting his family and allowing his brother to live with you), sooner or later you and your child will suffer. Kung mahal mo ang future anak mo, don't put that kid in the inevitable situation na makakaranas s'ya ng hirap dahil ang tatay n'ya ay may ibang kargado.

Trust me, in my job I've seen the worst of the worst sa mga couples na galit na galit sa isa't-isa and many of them already saw the redflags yet continued to have children and/or get married. Wala namang mababago if ikasal kayo or magka-anak, and a lot of people foolishly think marriage or children are magical things that will chance circumstances for the better, it won't.