Very evil times, indeed.
I'll tell you what you don't do. You don't debate them, you don't give them a platform from which to speak. These are not freedom of speech issues. Holocaust denial and the denial of the truth about 9/11 are acts of war, and should be treated as such.
What you should do, is expose their motives, expose their movements, reveal them for what they are. It should be illegal in America to deny the holocaust (as it is in Germany). And it should also be illegal to lie about 9/11.