A chord family consists of seven different unique chords that sound well when played together in a progression, with the eighth chord being the same as the first.
The major scale defines the name of the chords that will be played in the chord family. For example, when playing the C major chord, your root note is C. The C major scale notes would be C, D, E, F, G, A, B, C.
The chords played in a chord family would follow another pattern: major, minor, minor, major, major, minor, ‘diminished’, and back to major.
(In music theory, the half-diminished seventh chord is called a half-diminished chord or a minor seventh flat five).
So, the C major chord family would be:
C major, D minor, E minor, F major, G major, A minor, B diminished and back to C major.
There are 12 notes in the complete musical scale. Each note will have its unique chord family associated with the major scale based on the root note and will follow the chord family pattern stated above.