Is it true that goths and emos are devil worshippers?

No! of course they arent! your preacher is being silly and paranoid. You're brother will not try to kill you, you have nothing to fear. And most likely cults will leave you be, your brother is probably not a devil worshiper or in a cult; and ANYONE could worship the devil or be in a cult, not just goths or emos okay? hehe, and your brother was not made out of clay.