Capps. There specialty is 15 passenger vans and there are serveral in Houston. There is one on the Gulf Freeway just inside Beltway 8 on the east side of freeway. We use them all the time when we go to Mexico.
Enterprise rents 15 passenger vans but you have to call the local locations directly. If you are on the norhtwest side, there is an enterprise rental on hwy 290 feeder just past Jones Rd. I've rented there many times.