Make sure they have plenty of water. Put some water in the bathtub about enough to cover their paws, toss in a few waterproof balls and some ice cubes and entice them to go and play for awhile. Run fans for them, and if you can, have ice in front of the fans to cool the air. In Alaska, where I used to live, in the summertime it would get really hot, so I would drag a plastic pool in the house, set a block of ice in it, and run the fan with the breeze directed toward the block- when it all melted, I tossed in some toys and let my cats play. Worked great!