Houston is a good 5 hour drive EAST of San Antonio.
No. Try 3 hours, max, straight shot on IH-10. Which, in Texas, is not a long drive.
And San Antonio is not really South Texas. It's Central Texas. There are no law schools in South Texas. But there are no law schools in West Texas, either (Texas Tech, in Lubbock, is more in the Panhandle).