Mature orchids are a lot hardier than one might think if the roots are not damaged. Check one of the more dried out looking plants, take it gently out of the pot and check it to be sure the roots are still firm, but may only be a bit dried. If they are not soft, put back in pot and try to bring up the moisture level to what it was before when the plants looked healthy.
Depending on how long since the plants have been repotted, you may want to consider repotting in fresh mix, even though this is really not the best time of year to do so. Pictures of your plants would help for further answers to your problem. Hopefully it is just a lack of water and with more moisture, the problem will solve itself.
Good Luck,
Cym Ladye