"Each of the books of the NT has a separate author."
Little children in Sunday School know better than that.
Luke wrote the good message and the book of Acts of the Apostles.
John wrote the good message and letters I & II & III, and Revelation.
Paul wrote Romans, I Corinthians, II Corinthians, Galatians, Ephesians,
Philippians, Colossians, and Hebrews.