Welcome to the forum, thanks for the post.
have you tried making FullName2 a calculation like:
If (LastName2="";"";Title 2 & " " & First Name 2 & " " & Last Name 2)
so that you check for completeness prior to setting a value at all? That way, based on a failed check, FullName2 would stay blank.
You might even go as far as checking to see whether LastName2=LastName1 and merging Title 1 & " & " & Title 2 & " " & First Name 1 & " " & Last Name 1.
Is this what you're after?
Brilliance, works perfectly! Just needed someone brainier in filemaker then I!
Unitl they come along, I'm glad I could help.