I think that Kavalier Clay and Danielle Steel should create a new surname for themselves, by anagramming their two, existing surnames together and taking the longest word which emerges from the combining of their surnames' letters. Thereby bringing forth into the world:
Mr. Kavalier Catseye and Mrs. Danielle Catseye.
This newly-created surname would be used for social purposes and for family cohesiveness (as it would be passed on to any children born to them). I would suggest that they continue to use their original names for professional purposes, if either of them has already established a career for themselves prior to marriage.
Another reason for *both* of them changing their names… "Catseye" as a surname sounds way cooler than either Clay or Steel, anyway.