So after conferring with Katara's mun, there are more details!
Katara and Sokka are still siblings, and so they'll likely be seen together a bit. Sokka's dad is in the military, so they moved around tons while they were growing up (always giving up old friends and having to forge new ones), but he went missing recently, so the two of them are currently from a small town where their grandmother was their legal guardian. Their mother is obviously still dead. Because dear old dad is who knows where, Sokka has slacked off a little bit, and he's sure to hear no end of it from Katara.
Sokka will not be in a fraternity because, really, he doesn't see much point in that. (It's not real family anyway!) He's really good at math and can be a tutor to anyone, and he's certainly open to studying with any of the engineering majors on campus!
Update!
Katara and Sokka are still siblings, and so they'll likely be seen together a bit. Sokka's dad is in the military, so they moved around tons while they were growing up (always giving up old friends and having to forge new ones), but he went missing recently, so the two of them are currently from a small town where their grandmother was their legal guardian. Their mother is obviously still dead. Because dear old dad is who knows where, Sokka has slacked off a little bit, and he's sure to hear no end of it from Katara.
Sokka will not be in a fraternity because, really, he doesn't see much point in that. (It's not real family anyway!) He's really good at math and can be a tutor to anyone, and he's certainly open to studying with any of the engineering majors on campus!