What is a mountain disciple?

The great disciple stated by Master in Master's suicide note is the great disciple of Kaishan.

In the old law, only the first disciple can inherit the martial arts school after the master left, and only the first disciple can write (authentic boxing) on the signboard when opening in other places, and other disciples can't write the word authentic themselves.

The boxing taught by the disciple who started the mountain is also the closest to the master's boxing.

For example, in the past, the eldest son and grandson were also passed down at home. Is this to ensure family harmony and reduce contradictions? Now Japan, South Korea and North Korea still have this tradition.