Barbara wants to know how to deal with "you" when it's part of a compound subject or the compound object of a preposition. Should she say, "You and John are invited to the party" or "John and you are invited to the party"?

Barbara should say, "You and John are invited" because all pronouns (except I and me) normally come before the noun in compounds:

Compound subject: She and Bob climbed the steps.
Compound subject: Bob and I climbed the steps.
Compound object: She gave him and John an invitation.
Compound object: She gave John and me an invitation.