Let me break this down for you.
Up until this year I’ve lived in Brazil, specifically Sao Paulo, so I guess you could say I’m informed enough to address the question of the Brazilian tour groups. If you’re at least somewhat cultured, then I’d hope you’re aware of the financial situation in Brazil/ other third world countries- there’s usually a high upper class, and a low lower class. There’s hardly a midpoint, or a middle class; which is essentially a completely different can of worms, so I won’t bother to get into it. Thus, to provide you with some background, it’s the upper-class Brazilians that visit the United States twice a year, who are typically fairly wealthy. I’m not trying to be discriminatory, that’s just a fact. The lower class Brazilians can unfortunately hardly afford to live in Brazil, let alone travel to other countries and go to Disney (especially when we know how expensive Disney is.)
Anyways, Brazil is Brazil. I attended an International School, so I have a bit of a different perspective than someone who would have attended a private (or public) school, but from what I’ve gathered, Brazilians get sick of Brazil. Not all of them, of course, but when you can go to some of the nicest beaches in Brazil just over the weekend, the appeal of going to them might wear off. And with that being said, one of the most tourist friendly, ‘Brazilian’ places in America is Miami; which is practically a stone’s throw away from Disney. Instead of having three months off in the summer and a week in the winter, Brazil does a month and a half on each end. Which, in my opinion, is a much better way to break down vacations than the system the United States uses.. but that's irrelevant.
When you have a month and a half off for school break, it’s typical to fly to the Amazon for a week, or to Rio, or any other exotic place; and then retreat to America. Thus, the most crowded months would be January in the winter and July in the summer. Both take place in the center of the vacation period for Brazilians, so it makes sense for them to be in the US at that point, and keep in mind the seasons are swapped. Our winter is their summer, and so to escape the heat, the Brazilians go to Miami, where it’s hot but cool enough. And our summer is their winter, where it only gets to be 50 degrees or so, but that’s freezing for them. So they go to Miami, and then entertain themselves at WDW.
And the obnoxious behavior is behavior you’d experience with most tour groups. When you put a group of teenagers together, speaking from the perspective of a teenage, it’s bound to get a bit out of hand. So it’s really no surprise that the groups are annoying and rude; not to mention these kids are somewhat “wealthy”, and so depending on your opinion, they may or may not be more spoiled, and thus rowdier, than other kids. That’s very political, though.. don’t quote me on it.