Your vehicles will be registered in Polk County where the Escapees Rainbow Park / HQ is located.
Since you are bringing in near new vehicles from another state there will be some taxes due. Though Texas has an 8.25% sales tax almost everywhere the, the vehicle sales tax is 6.5%.
Over half the vehicles in Polk County are registered to addresses on Rainbow Drive, I.e. Escapees. As mentioned above, the Polk County DMV Office and Tax Office do this everyday of the work week.
Call the Escapees office and talk to them. They can answer almost all your questions or refer you to the person with answers.
Being members of Escapees and resident in Polk County make dealing with such items as you mentioned the easiest I've experienced in my life.
When you get to Livingston, Escapees has a checklist with places to go in which order to get things done. Takes less than 1/2 day to visit the offices and get everything completed.