Outstanding post, heaps of great information.
One question: You say Satan and Belezabul are one and the same. Does that mean they are not two separate beings, but the one God?
That means they are and are not at, at the same time, same being, but they are 'somehow' one.
Whatever one sees the other one sees , what the other is feeling is what the other one is feeling , is like two consciousness's emerged into one, but in harmony .
They are two two different beings but Satan is more then a Being , their case is and will forever be the only special one on this kind of matter.
Their are deeply and actually FULLY inter-connected and inseparable of each other.
Baal Zebul is Satan's brother after his father.
There's darkness and there's light , Satan symbolize more the Darkness and destruction part of it , the absolution , the beyond everything and Baal Zebul is the light , the one who could had seen within the darkness , the one who could See and Understand Satan and His concepts of everything , therefore they represent the Yin and Yang , the right and left arm.
Satan , from a non being perspective [which He is] is also the primary concept of all that has been founded upon, while Baal Zebul is the GOD of the Universe , Satan is beyond the universe , beyond any limits , think about this Satan is the subconsciousness [and not only that] and Zeus/Baal Zebul is the consciousness. Those two leading to what we have today 'mind' , not only mind but also a soul , a body , on many levels.
The realm of the dreams is unlimited , this is what beyond the Universe means, this is one of Father Satan realms , the infinitum on no conditions and limits and also Satan is the very dreams in itself , according to our own consciousness , we can only see and understand what we are 'limited' by our own self, the more we dive into spirituality and dreams, the more we understand of the Gods , mostly of Father Satan.
They are absolute because they are together , as it should be , leading to this universe working.
The other story is not as in literal as with them two GOD's , in their case, this is as in literal actual thing.
Just because someone calls on Satan that does not mean that Baal Zebul will automatically get involved , He will be there but not reacting at anyhow , same goes if someone calls upon on Baal Zebul , that would not mean Satan gets involved straight away , it will be only Baal Zebul , although they are One, They will be aware of you on the same kind of level regardless of which one would you contact. They 'guide' each other, and talk , understood each other.
Satan remains and is beyond GOD , I think GOD Baal Zebul , which is indeed the GOD of the entire Universe and the GOD of the GOD's and Humans , while Satan is beyond one foot away out of the Universe as HPZM said, Baal Zebul was the only one who could see , not only trough Satan as a being but to all of his very concept and everything that he represents, therefore , being the only one who could Fully understand Satan and emerging into him , made Him GOD , on his own very merit ,credit and power.
Baal Zebul is the one who deals with all of the matters within the Universe and Satan is the one who deals with all of the matters within the entire universe and BEYOND , mostly on the BEYOND matters of the universe.