They'll get there quicker if you bring them with you on the drive, and it'll be much cheaper. Overnighting large fish through UPS/FedEx is very expensive. The last box of six adult discus I sent was 20+ pounds and cost $150 to overnight. Plus you have to triple-bag them (at least) to keep their hard fin rays from puncturing the bags, then find a box and styro big enough, an oxygen tank to fill the bags, etc. It's way less complicated to put them in a styro or plastic cooler and throw them in the car with you.
People have mentioned air pumps, but your big concern on a 15 - 20 hour drive is probably ammonia build-up. If you have a cycled sponge filter, attach the battery powered air pump to that and it should take care of the ammonia for you. Otherwise, carry some Amquel or Prime.