As for showing your house, keep the kitties in a room with the door closed, with food, water, LB, toys, etc with a sign on the door in all CAPS saying "DO NOT OPEN DOOR". Make sure to tell the realtor to not open the door and the reason why. Take pictures of the room & post them on the door to the room.

I also put my cats in their room when the movers where loading my stuff onto their truck.

As for the two who have never been in a carrier before, a good trick to use is setting the carrier on end with the opening up. Then cradle the kitty one hand around the belly and the other holding the back legs together. Gently lower her into the carrier, and close the door. They may get mad and b**** about being in there, but they will settle down soon.