Sending out save the dates? How to address

My stepmom gave me the list of people they're inviting to the wedding and she want me to send save the dates

she wrote all the names like this

'Jimmy & Joan Smith'

not their full names - should I send the save the dates as

'Mr. & Mrs. James Smith'

or is that for the wedding invitation only?

I think you can pretty much do either one. I consider a STD less formal, so you dont have to do 'Mr. and Mrs'. Whichever one works fine.