1) Yes! I haven't talked about it too much, but my multiverse is an extensive, self-indulgent project I call the Astral Continuum. Eyl does indeed exist outside of time in what is called the Infinite Order, which is a catch-all term for dimensions beyond our reach (and even the reach of my eldritch OCs, who can only access fourteen dimensions). The only entity who managed to encounter Eyl is Lailah/Lyr-a-Lyl, but they kept Eyl's existence a secret.

Eyl is "currently" (relative to our perception of time) living on Etheirys as Ellevierre, Lee's neighbor. Neither he nor Iniare know Ellevierre is Eyl, but they will eventually.

2) Yisiel's fragments were born at separate times. The timeline is roughly: Yisiel fragments themself to escape being devoured by Abyss/Abyl (a black hole who sought vengeance) > their energy scatters across the Universe and just kind of wanders > with their physical body destroyed, Yisiel's consciousness takes refuge in the higher metaphysical dimensions > a mass extinction event catalyzes a surge of Yisiel's dispersed energy into coming together > Muse is born > thousands of years later, another mass extinction event eliminates 90% of humanity, providing yet another energy catalyst > Reverie is born.

Yisiel demanded these massive sacrifices in return for all of the energy they expended in creating this Universe. When Reverie vanquishes them, the hold Yisiel had on the remaining energy lifts, and the remaining two fragments (Arisel and Serenel) are born at their own pace without the extinctions.

3) I had to condense the terms because of character limit, but Equilibrium in the context of DoT (the story in question) refers to the balance between "emptiness" and "existence" (simply called Nothing and Something in this verse). It's another form of creation/destruction.

Celeste actually has three kids, Emile, Zuli, and Prism; Emile inherits Space, Zuli inherits Time, and Prism inherits a secret third thing. Ru Ya also has three kids, Lian Ru, Lei Qing, and Lan Hua; Lian Ru inherits Nothing, Lei Qing inherits Something, and Lan Hua inherits the same third thing as Prism. The secret third thing is called "Siphon" in my notes, but I'll be honest, I don't remember what it refers to.

These powers only apply to their relativity; because they are not in possession of higher dimensional power like, let's say Lee, none of them can alter other dimensions. They simply have control over gravity, a bit of time slowing/speeding, etc. Little basic things like that. The Nothing/Something is also limited to their respective world.

4) The components to Existence are called the Eternities: Chaos (who can be seen as Existence itself and is therefore its own component), the Void, Eyl aka the Bone of Life (the one who provides the energy for creation), the Breath of Life (the one who guards souls and memories), and the Blood of Life (the one who stimulates the flow of chaos and encourages evolution, growth, etc.)

Concepts like Death and Time do not necessarily exist throughout every dimension. For example, Death isn't really possible in a dimension as high as the Fourteenth, and Time is the Fourth Order that can be traveled as if it were an ocean. It's another direction in the way we can go up, down, left, right, etc.

5) Hyacinth exists in a different Universe than Haniel and Azrael! Hyacinth is from Dwelling of Tranquility (DoT) and the Dusk Seraphs are from Tears of Elysia (ToE). These are the project/story names. Technically, Hyacinth is what's called a Sainse [SAYNS], a mythical holy beast in DoT. I honestly might rename that term because I think Little Eros just took the word 'saint' and beat it up a bit.

6) Domenisela was created from pure eldritch blood by two Primordials, making them a purebred eldritch. Domenisela later developed worldly emotions and a soul from existing in the Third Dimension and expressed loneliness; in response, Somnilora was created by other Primordials from eldritch blood. Somnilora decided to make something of her own and used her blood, but Domenisela suggested that her offspring be able to integrate among mortals. Somnilora agreed, and Domenisela wept a single tear into her blood, thus creating Iniare with worldly emotions. In other words, Iniare is physically a higher dimensional god, but he has a soul (which the Primordials lack) and "human" sentiment. This makes him a hybrid, a cross between higher power and mortal sentiment. He's also referred to as a Paradox (Hyrrschyr in the Primordial tongue) or mutt (this is a derogatory term).

Ru Ya's origins differ because the metaphysical deities in DoT, called Dwellers, are not eldritch. They are merely gods that exist in another plane and have no set physical form, but they cannot access higher dimensions. Her father, Vissarion, entered this plane (Visre) by fasting and meditating until his soul temporarily left its physical body (in other ways he kind of... died, but was able to later return to his body because his fellow gods kept it intact). He then entered Visre, stole the powers of Nothing and Something, and inserted them into the body he previously created.

Truth be told, Vissarion had been intending to recreate a Dweller of his own, but it didn't work as intended. The body split into Ru Ya and her brother Jia Lin; Ru Ya retained 80% of Something and Nothing while Jia Lin kept the remaining 20%. Ru Ya also became part Dweller instead of full, but Jia Lin became an entirely different species (Cairaz, a vampiric species that feeds off blood and silver).

In DoT, the main lore is that the world suffered a dimensional rupture that created a parallel version of itself. The original world is dubbed the Origin, while the parallel is the Chasm. Parallel versions of every human are born in the Chasm and these are the Cairaz; technically, Jia Lin is Ru Ya's Cairaz counterpart, hence why he ended up that way.

To learn more about the Astral Continuum, I have a master doc here.