Try leaving your cat carrier open and in a common area of the house. You can even put treats or catnip in it, or spray in some Feliway. If you make it feel friendly for your cats, they will be less likely to put up a fight when it's time to travel. They might even hang out in it when they're just sitting around the house.

Warning: If you put a blanket in it, they might get a little too comfortable and urinate inside!