Addressing Envelopes

For my son`s bar mitzvah, I plan on using a single envelope.
How do I address the envelope if a couple is married but have two last names?

If a couple is married and has the same last name, is it ok to put Ms Jane Doe and Mr. John Doe or is it only proper to put Mr. And Mrs. John Doe?

If I am inviting a single individual and guest, and the individual`s child to I put -
Ms. Jane Doe and guest
Child`s name

If I`m using Mr. Or Mrs. For the adults on one line, do I have to use Master or Ms. For the children

How do I address the envelope for a single youth under the age of 16 yrs (male or female)?

Thanks.