They were right and it seems like you neighbors were cool, but the brother was being a *****e.
Further thought into the incident has revealed that my neighbor is not cool.
Before, I figured it could just be a family thing, you know? If your brother is in an argument, you typically stand by them. So I wrote it off.
However, after my girlfriend asked them to be quieter, and while the 2 other people were leaving, my neighbor got into his car and started honking the horn, honk after honk, for a good 30-40 seconds. We thought it was a car alarm but I looked out the window and our neighbor was sitting in his passenger seat, honking his horn. He was pointing towards his apartment and smiling, we assumed it was some weird thing they were doing.
However, looking back on it, we are pretty sure they were just trying to draw us out of our apartment. I can't think of a single reason why he would be honking his horn in regards to his brother or family, he also pointed at to our building, so it could have easily been our apartment he was pointing at as he walked away from his car, and this lead directly into the english speaking conversation my girlfriend and I overheard.
So as far as I can tell, my girlfriend asks them to not be so loud, 2 of the friends left, the neighbor got in his car and honked for awhile trying to bother us, then they both started yammering on about how out of line we were, and then we finally came out and the arguing started.
How childish is that? It's ridiculous.