Movie playing one cello with 4 people

Four stringed musical instruments play a sound because of one cello. I think that this performance method that seems to be a bit impossible, how exactly is it playing?

The movie is from the following.
Although there are four people, the sound is coming out normally.
YouTube - String Fever (Bolero)


This is a movie playing normally with one instrument each.
YouTube - String Fever (History of Music)


It is said that three brothers and cousins ​​are playing in this movie. Is it about Waza unique to your relatives?

Their official website is here. You can also see other movies from Video.

Stringfever - Welcome

There was also a photograph of the performer.

Eldest son, Giles Broadbent.


The second son, Ralph Broadbent.


The third son, Neal Broadbent.


Cousin, Graham Broadbent.


It seems that besides the eldest son, he can fight against evil organization.

· Additional notes
According to readers' suggestions, the first movie to play is cello. It is the difference between cello and violin, but since cello is larger than violin, he seems to play with a metal stick called the end pin adjusted in height and kneeled.