My younger brother(16) does not get along with my stepfather. This is mainly because my stepfather flat out just doesn't like him. I am 18 wanting to move out as well. Is there anyway I could adopt him or take custody?

Yes and no, depending on the circumstances. Where is your mother in all this? What about your father (not the step-father)? With the agreement of both of your parents, it is possible to get a guardianship done through the courts. Without the agreement of the court it's still possible to move out and have your brother live with you and have a power of attorney done up. If you are responsible and financially able, why not speak to both of your parents about moving out and having your brother live with you? You could enlist their help with guidelines/curfews/rules/chores, etc. that your brother needs and that you may not be prepared for.