abusive father. do I stay or go?

Im 17 and the oldest of 5 kids. My mom died two years ago when I was 15 in a car accident caused by a drunk driver. Ever since then it's just been my dad taking care of my younger siblings and I. My dad worked long hours 7 days a week when I was a kid so we saw him very seldomly so even though he lived with us I didn't know him all that well. Since my mom died he has been very bitter about being left alone to take care of us. He tells us all the time that he wishes he never had kids. Last year (on my mothers one year anniversary) he broke the news that he has been dating her best friend for 6 months. I wasn't happy but let it go. She has since moved into our house. Redecorated. Taken down all the family picture that include my mom. She has two kids of her own who are 10 and 12. They get treated like absolute royalty by my dad and his gf. My dad has taken to treating us like crap but buying really expensive nice gifts for his girlfriends kids and spending time with them etc but if we ask to spend time with us he says no. We live in the middle of the country and none of us drive yet so we rarely get out of the house. All of us spend the majority of our times in ours rooms if we're not at school. It was my birthday a couple of weeks ago and my dad offered to take me to the mall. I was really excited. He brought along his girlfriend of course and they spent the entire time picking out gifts for her kids whose birthday isn't for a month but got me nothing even though it was my actual birthday. When I told him I was upset about it he called me ungrateful and told me to grow up. He also never lets my siblings and myself talk about our mom so I feel like we never dealt with it. He has made us stop talking to my moms side of the family and never lets us see them or talk to them on the phone because he "never liked them". I cry everyday because I feel like he took all our our happiness away, he's just so horrible. Last night my siblings and I were watching a movie in my bedroom and I made us a bag of microwave popcorn. My dads gf came in and when she saw that we hadn't invited her kids to watch the movie too she called us all pigs turned off the movie, took the popcorn and told my dad she was moving out because us kids don't include her kids. My dad got PISSED and made me apologize and beg her to stay. Which I did because if I didn't he would be pissed. I'm so upset. He ended up getting upset anyway and pushed me up against the wall by my shoulders and stomped on my toe (I'm pretty sure it's broken). I ran out of the house crying and the chased me in their car screaming and yelling about how I needed to get the f**k back home or they would give me something to actually cry about. So I did. I was afraid if I didn't he would abuse my siblings and I couldn't let that happen. I really hate my life and feel so depressed all the time. I can't wait to leave for college and never look back but I also feel guilty leaving my siblings behind to deal with my father. My question is do you think I should go to college locally and stay home to protect my siblings or go away to a better college to get a good job so I can pay for them to have nice things in a few years? I'm so torn. My baby sister is only 4 and I swear my father doesn't give her (or any of us) the time of day. I feel like I need to be her mother figure. Sorry this post was so long and rambley.