Foster care/adoption question? Please help.?

[Angela]

I was adopted when I was only a few weeks old, (I won't say my age but I will say I'm between 12-16 years old) and I've basically known my whole life that I have 2 blood-related younger brothers (12 and 8 years old) and one step-brother (Maybe 4 years old). My birth parents separated after I was born, but still continued to have 2 other children, and then my birth mom had one more with another man.
I know as of today my birth parents do not communicate any longer and I know both of them aren't doing well. My birth father has gone to jail a few times and as far as I know, doesn't have custody of his kids.
My birth mother hasn't had a stable home and does drugs, and apparently "sells her body on the internet". She has contacted me through Facebook a few times, but I never respond because my family tells me not to. (My family knew my birth parents very well). Last time my family checked, my brothers have been living with other family members and have been moving very often.
So basically, my birth parents are a wreck.

I've heard my parents talking about trying to adopt my little brothers somehow, and I wanted to know if this was possible.
As an older sister, I want the best for my little brothers, and them constantly moving schools and homes is not what I want for them.
I was wondering if possibly my parents could adopt my younger brothers? Can anyone help me with this? Everyday this question passes through my mind, and I just need to see if it's at least possible.