family issues

I'm 20 years old & 8 months pregnant. My boyfriend & I live at my mother's house while we wait for our own house that we bought to get ready & moved into because the owner still lives there. anyways, a lot has been going on in this house hold & I just need to vent. I watch my 4 younger siblings plus a younger cousin of mine while my mother is at work & step dad works midnights so while he catches up on sleep, it's just me. I just recently found out that my mom has been cheating on my stepdad & need opinions as to what I should do & what I should say to My mom, because my stepdad knows & he took My little sister with him. My boyfriend & I are thinking about moving back into his mother's house until our house is ready because this is too much stress. but when I leave there will be no one to watch the kids while she works & my stepdad no longer stays with us. in need of some advice please.