Family problems and stepfather issues?????? help???

Hey guys, i'm a 19 year old male who has 3 younger brothers and 1 baby sister. our mother is a hard working, great person who is doing everything alone. she has a night job and it is making her tired, so she tried switching to days, but it was full. meanwhile, her boyfriend and the father of my 3 younger siblings has admitted to purposely giving her a hard time so she can have a heart attack and he can taker his kids to mexico..(he's illegal). i love my siblings with a passion, and my mother is the love of my life, and she told me that she will do her will soon, so he can't take the kids away. i don't even wanna think about anything happening to my mama.. i told her i'll look for a job to help her, but she insisted its not my job to do that... i'm a senor in high school and only have to go to one class from 1 till 3.. then i graduate. my plans were to move into my own place to start living my own life, because i don't wanna be held back anymore... but how can i when i know this stuff is going on????????
can someone please give me advice or help me on what we should do????