Who's Name Should Appear On A Headstone When Both Husband And Wife Are On The Same Stone?

In my view, the name of the both should be mentioned. You can start like;

Mr. Name of husband & Mrs. Name of wife followed by name of husband

Where i come from it would probably be as follows, ie John and Mary Smith(Nee Donnelly).

In cases like this, the last name is at the top of the stone, then the first names are under it one to a side You can even include the maiden name of your grandmother if you like as well as birth and death years. Depending of the size of the font or lettering you chose