Try this:
' Check for last, first middle (Doe, John P.)
^[a-zA-Z]+,\s[a-zA-Z]+\s[a-zA-Z]+.$
' Check for first middle last (John P. Doe)
^[a-zA-Z]+\s[a-zA-Z]+.\s[a-zA-Z]+$
' Check for first last (John Doe)
^[a-zA-Z]+\s[a-zA-Z]+$
and add one more else if for last, first of "Doe, John"
^[a-zA-Z]+,\s[a-zA-Z]+$