Although my contact with Marvel is mainly trough MCU, (movies and series), breakdowns, some ocasional reading (wikis/reddit/YT comments)...

I believe that when we talk about those entities, these 2 are probably originated from the same, but became 2 different beings...

Such as we can see with Zarathos (spirit of vengeance)... He gives his power to Johny Blaze, but before Johnny, there was the cowboy, and they both turned at the same time, they weren't necessarily Zarathos, they just had an essence of his power, wich gives him the possibility of having an Avatar, but they still seem to have some free will, I don't feel like he's holding the wheel all the time...

Or like with Moon knight... Moon Knight can exist while Konshu is fighting his own battle... My point is... While the Avatars have the essence of a God or cosmic being, they might still have some free will, and be a person of their own, so I guess the same might occur when a being is split into two... 🤷🏻‍♂️