I am no Miss Manners, but here is my opinion:
When you address an envelope to a married woman, 'Mrs.' is appropriate
only if the name appears in the form "Mrs. James Johnson" (meaning the
wife of James Johnson). If the woman's own first name is used in any
form, 'Ms.' is the title to choose: "Ms. Janet Johnson." There is
usually no such thing as "Mrs. Janet Johnson" except in the case of a
woman who is married to another woman.
If you are sending an invitation to both James and Janet, and they
have the same surname, you should use "Mr. and Mrs. James Johnson,"
even if Janet is using her maiden name as a middle name (without
hyphenation). If Janet kept her maiden name of Jones as a surname, you
should use "Mr. James Johnson and Ms. Janet Jones." If Janet created a
hyphenated surname which James does not share, you should use "Mr.
James Johnson and Ms. Janet Jones-Johnson." If both James and Janet
use the same hyphenated surname, you should use "Mr. and Mrs. James
Jones-Johnson." If they are using different hyphenated surnames, you
should use "Mr. James Johnson-Jones and Ms. Janet Jones-Johnson."
Frankly, I like to dispense with titles entirely. I find nothing rude
in an envelope that is addressed to "James and Janet Johnson," without