Combining Cells for an Address

Hey there,

I am taking a database file of customers where there are two people listed as the purchasers and sending out a New Year's card. I'd like to combine the cells of the two customers to where it on the address it will say "First & First Last" but I also know that not all of our customers share the same surname. How can I set up a formula to where it will combine the information to say "First & First Last" if they share that surname but also recognize when the surname isn't the same and create "First Last & First Last"?