Hey Samantha my name is Jeramy and I am 26. I have had "at least Ifrom what it sounds like" a very similar life to your's. I am the oldest as well.
You have probably heard that it will all get better. Well the truth is that things can get better and sometimes somethings do and will for you. But things will still be crappy for the most part. But this is what I wanted to tell you. Becuase you are dealing with what you are dealing with you WILL be a better person for it.
I never thought finding guy so have sex with my mom for any money that she could get would make me stronger in life but, when you wake up the next day and find both of them naked in the living room floor with needles in their arms and YOU have to take care of them so you two little brothers and little sister does not see them.
After you do things like taht you really can get through much more then any stupid ass with a "normal" childhood.
I hope that you have friends wherever you are now. That is all that got me through my childhood. That and music.
If you need anyone to vent to or any advise my MySpace is http://www.myspace.com/jeramyspicer27