You should get the first and last name of every guest. It’s not appropriate to put Mr. John Smith and Guest or as we recently received on an invitation, “& Spouse”. In the situation where it’s a married couple, Mr. & Mrs. Smith is fine -- unless of course the wife has a different last name or she has a professional title such as Dr., Hon. Or is in the armed services and then she would be listed first.
There’s nothing wrong with sending an email or calling a guest and asking for the correct spelling of everyone’s names or asking a guest brining a date you’e never met for his or her name.