They are probably real to the minds of those who believe in them, in reality they are either small in number and not a threat to anyone or are very good at hiding themselves. As for them brainwashing people, I think people can be brainwashed but not in the context of a brainwashing machine that someone goes into and comes out with a completely different ideology and personality. People can be "brainwashed" by culture, and by society, by this I mean that by growing up in a society most people generally are conformist and accept the ideology and thoughts of the society they come from. Kind of like how a lot of Americans aggressively hate everyone and everything from the middle east when they lack an understanding of what they are talking about (ie a lot of Americans on the street would say they favor nuking or at least bombing Iraq, when almost none of them can locate it on a map). When people have opinions on things they don't understand, they are "brainwashed" to some extent by the people who indoctrinated them with those beliefs or ideas in the first place. But as for the Illuminati, I have not seen sufficient evidence to affirm their current presence and conspiracy plots, they have existed in the past, that has been verified so they are real, just maybe not active as far as I Know.

I recommend researching for yourself, not one answer on here will be long enough to completely explain the complexity of those that conspire to dominate the worlds politics, even after ~7 years of research, there are many questions left unanswered.

Google "illumanti structure" and go from there.

This is the most realistic structure I've seens so far: http://bit.ly/g37p3H