Hmm I'm curious dear you seem to have many magical creatures in the loop
How do you categorize them

My own arbitrary attributes
I would often put demons on an infernal spectrum (Hellish like realms but not exactly evil or cruel but can have a tendency but many can care alot about freedom and good will)
I often put myself in the opposite area celestial (Likely paradise like realm not exactly good or benevolent and even some can be over objectivists)

If you are asking for my general opinion on what makes one, that may be difficult for me. Let's see, to me I'd define a demon as "an unreal entity seen by many in a negative light/Foreboding". I think. Origin of said demon can be from anywhere or any thing. To me it is more like a "Status" or "state of" in something's existence. To have another specification set in place, a demon is also not a beast, but a beast can be a demon. It seems that things I call a Demon seems to have a focus on being "overwhelming" in some manner as well. Evil does not need to be a requirement to make a demon, but is a common trait and a common label.

To add in something defined, I do not consider Uluri's beast form as a Demon Form for a reason. She's not overwhelming enough. She might seem unreal, and of a negative light, but at max she's a monster. Not at a high enough status to be considered a demon in my eyes.

While in the opposite entity would be: Unreal, Seen in a positive light/enchanting, Overwhelming.

*Sat down and thought about this for 2 hours, but unsure if this answer is good enough. Was really difficult for me to think about.
*added: Efret and Sin are a species of Demon; Born with a status of demon, in other words, Born with that which is Overwhelming. A War Demon and Incubus.
* JUST PRESSES ENTER SO THAT I CAN RESPOND> Bageezums me. You take forever to think!!!

Well thanks dear