Who and what are the members of CP 0? In One Piece during the dressrosa arc, it is shown that members of the world government's CP 0 were present on the island. 

What exactly is CP 0? 
Does this mean there is a CP 1 - 8 as well? 

And if they were stronger than CP 9, how did some of them end up turning into toys? 

I am current on the anime and manga and don't mind spoilers. I'm just confused about this.
As per One Piece Wiki:

So far, the CP agencies seen on the Grand Line are CP5, CP6, CP7, CP9 and CP-0.
There are eight official Cipher Pols that are numbered from CP1 to CP8 with two unofficial units, which are named CP9 and CP-0 . Cipher Pol No. 9 has the license to kill any citizen that does not cooperate with the World Government or acts in contrary to its interests. Because such a radical method of applying justice by the World Government should not be common knowledge, this group is a top secret organization. CP-0 is apparently more powerful than the CP9 as they are called the world's strongest intelligence.

-CP-0, more properly known as Cipher Pol Aigis Zero is the strongest intelligence organization among Cipher Pol, according to Nico Robin.
-None of the CP-0 members were turned into toys. Although, Doflamingo does have control over them.

Doflamingo revealed to Law that he was granted authority to command CP-0 because he holds secret information about Mariejois' 'national treasure', which will shake the world if its existence is revealed to the public.

You can read about them in detail here