Joseph Kavinsky Edit
Joseph Kavinsky is Mrs. Kavinsky's son. They are not seen together in canon and nothing is known about their relationship outside of speculation.
Mr. Kavinsky Edit
There is nothing known about Mr. and Mrs. Kavinsky's relationship, but one can assume there might be some stress since Mrs. Kavinsky lives in Henrietta with Joseph instead of with Mr. Kavinsky (assuming Ronan's was correct in thinking Joseph was sent to Aglionby Academy because of his alleged attempt to kill his father).
The Gray Man Edit
When Mr. Gray is investigating the Kavinsky mansion while looking for the Greywaren, he finds a "house full of wonders". He stumbles across Mrs. Kavinsky in the bathroom vomiting. He tells her he is a figment of her imagination and she accepts it without question, likely because she's high on cocaine.