they take into account any income you make as well as the income of your legal guardian. not sure if that's your brother or not. and if the total of that is <$30,000 then i think you'd qualify. unfortunately, i did not qualify and had to put it all on a credit card which i will be paying back for a long time. one good thing, i guess, is that they tell you pretty much immediately if you qualify or not. for something this specific, i would say that you should get in touch with AMCAS directly. i'm assuming that you want to apply for the fee waiver before you sign up to take the MCAT, yeah? and then you would apply next june? it's unclear from your original comment where you are in the process.
anyways, good luck!