I'd suggest:
1. Adapt them to traveling in a car before the trip as posted, it's a one time thing for us that worked for on every cat.
2. See the vet, there are meds that calm cats. Our current cat has brain neutrons that misfire and he a total terror when they cut his nails. We can't do it and very few vets have the required skill - Yes we've tried multiple vets during our travels. He now gets a med the night before and the morning before.
3. Board them.
4. Full harness and leash. Also have the ID device inserted in them.