If you do determine that it has the V-belts, the following P/Ns should get you started in the right direction.
Power Steering and Water Pump Belt: Carquest 17465
Alternator Belt (driven off A/C Compressor): Carquest 15290
A/C Belt: Gates 9570
There are what I used on my '83. These numbers should be able to be crossed to other equivalent P/Ns at any auto parts store.
Above and beyond belts, I'd have your family members take a decent look at the tires to check their ages...
https://www.youtube.com/watch?v=S_VYhD49fjk...and absolutely make sure there's an inflated spare tire present. If there's any questions about tire condition, take the conservative route and replace the tire(s). The stock tire sizes for these cars are cheap and can be found basically anywhere.
CA to TX would likely be a pretty tough drive for any older vehicle, but if it were mine, I'd do the following prior...
--Full engine oil/filter change, and chassis lube to include driveshaft u-joints. Check for play or "clunking" in the u-joints that would imply worn/missing bearings.
--Check coolant level. Drain and replace coolant if there's any question of cleanliness, but DO NOT FLUSH the coolant system.
--Change transmission fluid and filter if the ATF is any color but red, but again, DO NOT FLUSH the transmission.
--Check transfer case oil level and add ATF as necessary.
--Check the rear differential oil level and add as necessary. No real reason to change this unless you can see evidence of serious contamination, like water in the oil that would make it a milky-brown color.
I'd recommend leaving the car in 2wd for the trip, and because of that, I'd leave the front differential alone if you see no evidence of major oil leaks. But the advice for it is the same as the rear differential if you desire, check the differential oil level and add as necessary.
If you've gone this far with it, it shouldn't be a huge deal to pull at least (1) wheel off the front and back to check the condition of the brake pads and shoes. If you have any brake hydraulics components leaking, they should absolutely be replaced, preferably in pairs because we're likely dealing with 30+ year-old parts. (If one front caliper leaking, change them both, as the "good" one is likely not much better than the leaking one. Bleeding two calipers isn't really any harder than bleeding one.)
The safety items (belts, tires, brakes, etc.) should have been part of the CA vehicle inspection, so hopefully you can trust that inspection, which is probably one of the most-strict in the country.
As for the last thing, it would be a good idea to have your family assemble a basic tool kit to take with them including a US & Metric socket set, screwdrivers, pliers, baling wire, and a couple quarts of engine oil, ATF and gallons of water. And probably a AAA membership...
Good luck with the trip, and of course, thank you for your service. Stay safe!
David