Is this just the tripple A rated Bethesda writing striking again or am I missing something but you can give Nocturnal your soul AND still be a werewolf what means that Hircine has your soul at the same tim.
Am I just forgetting something or is this really just what I said it could it be in the last sentence?

ha i think you also swear your soul to namira, in dawnguard your soul gets trapped in the soul cairn, you're promised a return to sovngarde, and since you're dragonborn doesnt that mean you have the soul of a dragon?

apparently your soul will be split in 5 pieces or so once you're dead

I don't think it's meant so literal.

You still have your soul, it's just that you have dedicated it to a Daedric Prince. It seems quite characteristic of the Princes (and TES Lore in general) that "giving them your soul" would have loop holes in it, and that they would fight over who controlled your actions and deeds, (ei, your soul)

Souls are very malleable in the Lore. They can be trapped, deformed, cut into pieces, etc.

Besides, if you finish the Thieves Guild questline your soul no longer belongs to Nocturnal because you held up your bargain. At least, that's what I remember.

But it would be very interesting to see a bunch of daedra fight over the Dragonborn as their champion/slave.

this is the only proper way to imagine it.

I get what you mean but you have to cure that old Companion guy from Hircines curse so he can go to Sovngard (hope I wrote that right) and that means that as long as you have lycanthropia you'll owe Hircine your sole, then you lose a part of it in the Soul Cairn and (probably) that same sould to Nocturnal.
Even if it's ment to be symbolical, it doesn't make too much sense to me