They'll probably survive in Houston if you plant them in a sunny spot, sheltered from north winds and weather. Vanderplank's book says they can tolerate temps down to 32 degrees, but I've found his estimates to be somewhat on the conservative side. If you get a hard freeze, you may well lose them, but in Houston the hard cold snaps never stick around long.

I've found that with my Incense, if the plant gets bushy, the extra vegetation acts as insulation and protects the plant from freezes. Alata's a larger vine, so it has the potential to develop a thick layer of protection. You can also cover it with a blanket on expected cold nights. Other people string Christmas lights in the plants for added warmth.

The Ulmer & MacDougal book says that Alata planted in the ground will get large, but may be reluctant to flower for up to two years, as it will put much of its energy into root growth. If I were you, I'd try to establish cuttings of these plants and overwinter them indoors just in case your outside, in-ground Alatas don't make it through February.

I'm in MD so mine are container grown. My P. alata doesn't get as bushy as many of my other passies. It does have a much thicker stem and big leaves but the only way I get it to branch is to pinch the growth tip. It flowers later in the season then many of my others and doesn't produce as many blooms but what a bloom! It roots very easily in water with bottom heat for me. I'd take jblaschke's advice and take cuttings to root before the cold sets in. I feed it infrequently and dig in a little bit of chopped banana peels every 4-6 weeks. It's in full morning sun and dappled afternoon sun. I water it when the foliage starts looking droopy. You'll love this passie. I think it has one of the prettiest blooms.
Karyn