Vacuum, vacuum, vacuum. Then vacuum more. HEPA filters are considered to be the best for picking up tiny dander. The addition of a few quality air filters will also reduce the amount of dander and other allergens to be dealt with. If the air quality is poor in your house, or especially dry, it will aggravate dander even further.
Dander easily becomes airborne and can get into the smallest and most unlikely places.
Your cat s diet may also be affecting their skin and coat, so be sure they have a high protein, quality diet. Substances like Allerpet C can be used on cat's fur to dissolve some of the dander and protein from the saliva that people are allergic to as well. The longhaired cats have more area to deposit their saliva on and brushing helps, though it puts more dander in the air, so shorthaired cats tend to be better for people with allergies. Some people are simply allergic to new cats. This kind of allergy will tend to diminish with repeated exposure.