I believe we only have one responsibility when we are born, to become ourselves. When we get old enough to see more clearly, have some experience under our belt, we can choose what to keep of what we have "learned". Just because it comes from our family does not make it right or something of value to us! The real advantage families have is that we're a captive audience for more years than we are to most other things.
Being "Southern" in the way you are now, is a choice. It's a little like being an "artist" or "writer" or identifying with anything else and calling it "mine". Because you have been ingrained to be super close does not mean you necessarily have to stay super close. Your brother is your parents' and his own problem, not yours. You can choose to make him yours or you can choose to walk away or your can choose something in-between, etc.
We pick up good and bad habits from our childhood and those we are raised by/with. But the bulk of what makes them "good" or "bad" is our deciding they do/do not fit with what we want and need, ourselves, in our individual lives.
My therapist was, literally, a whole different nationality, so could not begin to understand my growing up. I was sexually abused by a man of her nationality (made therapy a little dicey for awhile, that did :-) but whether someone "understands" us exactly or not is not really one of the goals of therapy, I don't think. We have to understand ourselves and how we relate to others, not particularly other people's quirks and orientations.
My father's father came from a line of northerners from Minnesota and the northeast and my father's mother was born and raised in Asheville, North Carolina, her grandfather fighting on the South's side, his on the North. Their marriage didn't work out very well and sometimes I fantasize about whether their family backgrounds could have contributed to that