Traveling with 2 nervous cats
Later this year I'll be moving with 2 elderly, nervous indoor cats. Even the current short walk to the vets has them howling and shuddering. For the move I'll be traveling by taxi and then 1.5 hours by high-speed rail, only to put them into entirely new surroundings. They won't be happy.
I already know about all the prep, their smells, introducing them to the new space, etc. but I'm very worried about the travel.
What are some things i can do, supplements i could give, that would help them calm down even just a little. Obviously during the trip all my attention will be on them, but I'm honestly worried they'll stress themselves out too much.
(15 year old sham-tabbies M and F, heavily imprinted on and devoted to me, indoors only)