Eco PCO ACU may be applied if pets are in the house, however we would recommend refraining from spraying any insecticides while pets are in the same room. You want to wait until applications are dry before allowing pets to re-enter the area. Eco PCO ACU is not, however, an appropriate treatment for fleas. We recommend our Indoor Flea Kit for your situation. You want to keep pets out of the treatment area until the application is complete and dry.
A very gently product for use on the cats themselves would be Greenway Formula 7 Dog and Cat Flea and Tick Spray.
The System III should be compatible with any type of aerosol including the Eco PCO ACU.