belief in all of them is important because they were all sent by God
it is written in the Qur’an that we should make no distinction between them, al Baqarah,2:285.
the Qur’an tells us stories of the various prophets of God sent over the ages which makes it imperative for a Muslim to believe in all of them as a Muslim cannot challenge what the Qur’an states and still be called a Muslim.