If it's a reply to a wedding intivation, one traditionally writes in longhand, with these line breaks (I hope they come thru) Mr. and Mrs. Jones accept with pleasure the kind invitation of Mr. and Mrs. Smith To decline an invitation, Mr. and Mrs. Jones regret exceedingly the kind invitation of Mr. and Mrs. Smith.
Ms
Mr and Mrs
The word for Mrs. is "pani" and is pronounced pahn-yee. The word for Mr. is "pan" and is pronounced pahn.
Mr and Mrs is correct or Mrs and Mr is correct
Potatoes
an assassin
Mr. and Mrs. (ex. "Hello, Mr. and Mrs. Evans" instead of "Hello, Mrs. and Mr. Evans")
Mr. & Mrs. Smith
Kind.
The original terms are Master and Mistress, abbreviated as Mr. and Mrs. Nowadays, we say Mister and Missus.
Yes, Mrs. has a period because it is an abbreviation and mrs is not a word. The same holds true for Mr., Dr., and Ms.