Im 18 n my mom is a drug addict and my step dad is an acoholic. My brothers are 12 and 10 and have never been in school. They do not know how to read,write, nor spell! They are in a home where there is a lot of prescription pills and alcohol that they get into. Is their anyway I can get custody of them? I have a stable home a job and can get them in school.

Call the cops!
It is illegal for a child not to go to school (Expecially where I live), try asking your parents if your brothers can live with you. GET THEM OUT ASAP! This is very harmful for them and they will suffer there entire life if nothing happens. If you can get grandparents, aunts, uncles, anyone who you trust to help! They may not award you custody but they may let another family member take them!

You can petition the Court for custody if your parents will not consent. If you can prove you have a place to live, are stable, have financial security, you very well could be awarded custody.

How is it that they are not attending school and no one realizes it?

If they are being subject to abuse - they have access to pills and alcohol - then the child protective services office in your area should be notified.