House cat exposure to vaccinated kitten

Question
We have two 5 year old house cats who have not left the house for 4 years, then to the vet for shots.  Their shots are not current. My son,who lives in his own apartment, has a new kitten with all its shots.  The kitten has never been outside, or with other animals since leaving its litter. My son is having elective surgery, and it would be convenient if he recovers for several days at my home. The question is, would my cats be at risk if the kitten was brought into my home for these few days?

Answer
Well, I am a bit confused by your sentence about them not leaving the house for 4 years then to the vets for shots.

I would say that neither the cats nor the kitten are at risk but if anyone was at risk it would be the kitten from two non-vaccinated cats. Cats can get leukemia through the screen door if a cat with it sat at the screen and hissed at them. So being indoors doesn't protect the cats.

Keep the kitten in a room with your son and a litter box, water and food and everyone should be fine. He will need more than the one set of vaccinations so maybe you can take the kitten in if he is due by the time your son is there.
A speedy recovery to your son!