I have 6 cats. When there are so many cats in one house, there is a lot of hair and dander flying around. If you have carpets or sofa's, coyches---they can retain dust mites and dander.
Brush your cats more frequently, a tad of canola oil on 1 paw, vacuum your carpets, furniture more often.
The most important thing is just to brush your pets thourouly more frequently.