I hate my stepmom! please help.?

I'm 15 years old and i have a sister who is 14 and my parents got divorced when i was in 1st grade. My dad married my stepmom and now they have three kids, i love them so much don't get me wrong. But i cannot stand my stepmom, she is 16 yrs younger than my dad and so she is VERY immature, she only is civil to us because of my dad. We've gotten in some pretty big fights even when i was much younger, she always gets mad whenever my dad wants to do stuff with just me and my sister. My dad's family is muslim and my mom is catholic so they have different cultures you know, my stepmom is muslim too and she is young which causes her to be very jealous and immature. We moved to a different state about three years ago and we visit my dad about three times a year, and as much as i miss him and the rest of my family i can't help but dread it because of my stepmom, i hate going into the house where MY dad pays ALL of the bills and i knew him before she did and she makes me feel like an outsider in my dad's house. and i love my half bros and sis, but it makes me mad sometimes when they're like this big family, and if my stepmom took that from me, then why can't she be nice to me and my sister? but anyways, me and my sis are flying there for a little over a week, and i'm excited to see my dad but i don't want to see my stepmom, it sucks, it's been like this since i was eight. and i'll be getting my license in 2 months and do you think it would be bratty of me to ask my dad for a car? and i just don't know what i should do...is this normal? and when she is a b*** to me i can be one back to her right?