Thanks to everyone for your support and concern, it helps a lot.
Here's what I know so far:
As of Sunday my mom and little brother were going to a local shelter. If it was full, they were going to an aunt's place in Alabama. I've spoken to that aunt now, and she says my mom never showed up, so that means she went to the shelter. I don't know which shelter, and how the shelters fared in the storm. I'm operating under the assumption that they're OK, my mom being the ultimate survivor, and my little brother being the craftiest 14 year-old ever, but their home and car is long gone (which is everything they own).
Alternately, I'm freaking the fuck out.
Also: one aunt and uncle evacuated in Montgomery. Two cousins made it to Texas. Another cousin in northern Mississippi. All homes and apartments lost.
Are all of your people OK?