My cats on a road trip are they safe from winter cold?

My brother made a 14 hr trip from Louisville ky to Texas to pick up my two cats because I was unable to due to work. they have been set up with a carrier tent material and water and fur material pillow and kitty litter. He had to stop midway in the trip but kept them in the car with no food in about 30 to 40 degree weather. Will they get sick from overnight stay in car he wasnt able to move them to the hotel for the night because he is allergic and doesnt know how to handle cats.