Kingdom Hearts II Organisation 13 and Darkness?

I'm curious.
Organisation 13 members are Nobodies, said to exist as beings of neither light 'nor dark. So how come they can use the darkness to come and go as they please?

Also, how can they summon the heartless? That really got me confused.

 

if you played CM on rikus story it DOES say that they are neither light or dark yet it sqys that they drift in the middle of light and darkness

 

The heartless ally with whoever is the strongest, but that's always been on my mind too if sora is the strongest he should be able to control heartless

then again they wouldnt ally with the person that destroys them

 

I think that even though nobodies are not from light or darkness they can still use the powers of darkness. For them they can use the corridor of darkness easily because they have no hearts and the darkness cannot harm them

the heartless most likely don't join Sora because he has the keyblade