Hauling 14 hours should be no problem since you will probably stop several times en route to re-fuel, potty break, food, etc. They will rest some when trailer not moving (if they haven't lain down in trailer).
You should definitely have a "Vet's Certificate" (traveling papers) covering all of the animals. Since they're heifers, they should already have had their brucellosis vaccinations and ear tags. If they haven't been vaccinated for brucellosis, have that done as soon as you get them home---have Vet come out or take them to the Vet (only a Vet is allowed to do this).
If you do not get written proof the cattle were current on de-worming and all vaccinations, you can assume it hasn't been done ("verbal orders don't go" to quote an old maxim).
When you get them home, quarantine them in a pen for couple of weeks to check for any health problems. If you suspect "shipping fever", vaccinate them and/or treat them for this while in quarantine. I would also de-worm them upon arrival at your place (as an extra precaution).
If the seller says "I don't vaccinate my animals" or "yeah...they were vaccinated (but can't give you any details) suspect that it was not done.
Note: Some States have strict import laws regarding Brucellosis and TB. Texas is one of them. Be aware of this. Don't know about your area. If your area is "exempt status" or the seller's area is "exempt status" that just applies to the STATE, not the seller's herd per se. If you don't have proof, re-test.