what is the family name?
SELECT  T1.family_name  FROM Course_Authors_and_Tutors AS T1 JOIN Courses AS T2 ON T1.author_id   =   T2.author_id GROUP BY T2.author_id ORDER BY COUNT ( * )  DESC LIMIT 1
family name refers to T1.family_name; family name of the author who teaches the most courses refers to ordering by COUNT(*) DESC and selecting the top result;