There are many kinds and sizes of Chinese painting brush. Mostly they are made of animal hair, range from wolf, sheep, cow ear, horse, chicken, rabbit, pig, yellow weasel, you name it. Some people make brush out of baby's first hair as a life souvenir.
Different brushes, as in water colour or oil painting, are used to serve different purpose.
I buy all my brushes myself. Everytime I go back home in Beijing, I go to art shops to buy one sample and take back home to try. When it is good, I buy hundreds for my class until I visit home again.
By the way, the knife in the middle of the brushes is for cutting paper. It is not made of any hair.