Duke and Duchess of Cambridge?

[fluter]

My family would find it downright quaint, and they would laugh at it. It's sexist as well.

Hrmmm, what's sexist is the title "Mistress" itself, not so much its particular application. (he pontificated, pedantically )

In this country the usage "Mrs. Husband Surname" is correct, but almost extinct through simple ignorance. If in doubt, or if the lady does not choose to change her name, there is "Ms."---which in my part of the world, is generally pronounced the same as "Mrs." I.e. "mizz."

Regionally: Susan Jones, the wife of James Jones, is more frequently called "Miss Susan" than "Mrs. James Jones."