They all started as humans who like Apostles sacrificed their loved ones to become demons. However, the God Hand were chosen specifically chosen by the Idea of Evil to serve as its purpose for suffering. Instead of the regular Behelit, They used the Crimson Behelit to sacrifice a large group of their followers in order to transcend their humanity. Their Behelit is also called the "Egg of the King". All of the God Hand are worshipped by Apostles, even the most powerful of them must submit to their authority. The God Hand are so powerful they cannot easily take form in the human world. They usually enter through short lived constructs made from anything they want.
The five members are:
Void: The leader, and has to do with the destiny of all.
Griffith (or Femto): Can warp space.
Slan: Clearly lust and pain.
Ubik: Likely has to do with dreams and manipulation.
Conrad: He seems to represent death and disease.