Your cats might have mites or fleas. Do they go outside or do they have contact with other animals? If you take your cats to your veterinarian, he or she can check for external parasites. Have you begun using any new cleaning products? Sometimes contact with chemical residue causes dermatitis. It is allergy season so that is another possibility.
The homeopathic DERMA-IONX can help with the symptoms of itchy skin and hair loss. But you also need to determine the cause. I also like to give PROBIOTICS and OMEGA 3,6,9 when there are skin symptoms. They work well together with DERMA-IONX.
Please let us know if you have any other questions.