The Ones of Mortis are many things, but most of all they are undefined, designed to be more than one thing at a time and serve more than one story purpose. Hence, what are they to you? Gods? The Force transcends everything, so how would actual literal gods even work within or above it? While godly, these beings are not en par with the Force or a unified God but themselves were limited tools of the Force despite their power. And if appearing to each who visits them different, befitting the viewers own species and form as per Book of Sith, they may have no fixed form at all. What if that is not just their shape but also their entire being? Is the number fixed to 3? Could it be 5 or 7 or 1 at other times befitting a visitors needs and story? Genders fluid even so another trinity can also be them? Mother, Maiden, Crone of Dathomir? How about the Force Priestesses Yoda visited? Is anything about them even fixeable or is all in flux as the Force wills it? Celestials or what Celestials become? Legends merged its Celestial concept with them, and made them Celestial and yet more than that. In a way even that only Celestials could become like them and the same process required would transform others trying to into monsters like Abeloth and others. Shapeshifting Forcewielder Species? Given the shapeshifting and flux of their appearances, are they even a species? Or is Forcewielder just a general term for "entity of non-fixed form that uses the Force"? Avatars of the Force? Are they physical Avatars that took on the roles the Force required them to serve or are they Avatars in the sense of a mere projection of the Force itself? Ascended Mortals from the time of that Jedi signal they used, 2000 years ago (early NSW, Darth Ruin era)? This one is interesting. While Legends went with them being superancient to account for several Abeloth escapes and re-imprisonments, actually their age and story could be quite different. If mortal beings ascended somehow to these roles, could it be the last to do so was around 2000 years ago during Darth Ruin's era? If they are a Jedi family from that time, their story takes place right at the beginning of Lucas own headcanon timeline with Darth Ruin and the Sith beginning to dominate the galaxy. Free of Legends and canon baggage, tying them into that story would be an interesting minimalistic take with everything Mortis related much younger than previously thought. What if the Mortis roles changed over several ages, or the people inhabiting them did switch and the current trio is not the original one? The Prime Jedi and his children from Ahch-to? Maybe the Prime Jedi and his children were the first Mortis Ones. Maybe the Ones we saw are those from Ahch-to! Though Rebels seems to imply that the Ones are connected to Lothal and the Force Priestess on her world. Whills? Are they microbiotic or macrobiotic entities that showed the microcosm of the Force to Anakin and co in a way they would understand it, much like the Force Priestess did to Yoda? Hence, the inside out moment of both the Force Worlds inside or Mortis Monoliths inside being "bigger on the inside" and a teaching tool, magnifying what is important within each one of us. The previous Chosen One and his children seeking to be replaced? As a paralell to Anakin and his twin children, as well as his life story entire, the Mortis Ones seem to be made up befitting what he needs to see and hear. There is no Mother or she is dead, Anakin a Father with twin children alive. Likewise Shmi was the mother of him and there was no Father but the Force, who these represent are his parents. They could playact this entire Mortis scenario in TCW just for him. Including the deaths. Did they even really die or can they? Maybe they just faked it and are very much alive. As Morai, Bendu and the like seem to hint at in yet other forms they could have taken easily. Then again, maybe this is an Indiana Jones and the Last Crusade Knight Templar scenario, a mystical place granting immortality so long one fulfills a duty on site. And the last Knight, the Father, seeks replacement now but Anakin denies it and is not ready, yet. Thus, are the Ones even truly dead? Do they even need replacement? Are they still around in some shape or form?
My personal preference is for them as Avatars of specific aspects of the Force; a kind of Force Ghost++. Perhaps they were mortal being(s) once, but that was so long ago that now they are more vessels that the force flows&acts through rather than individuals, similar to the Force Priestess(es) over time becoming split into different aspects of herself. As a side note, I'd like it if we saw reincarnations or alternative forms that in which the Father manifests instead as the Parent, so that the hole of a mother is no longer open. I prefer this to adding a 4th Mortis god because the trinity setup of characters is pretty integral to a lot of Star Wars' storytelling and theming
Honestly I see the Ones and the entirety of the Mortis arc in TCW as being figurative/metaphorical and not something to be taken literally. (Looking at you Troy Denning) Essentially an extended Dagobah cave sequence, except on this weird space Monolith.
Indeed, most would say how can one fall to a side one represents, but that is missing the point. While there is a narrative shift between the second/third episodes and the very first where they are more metaphysical compared to their deconstructed selfs in the latter episodes. I think this shows that while they serve the function as avatars, they are not just avatars or had not always been indeed. The question though remains if they all payact the happenings for the visitors to understand a point, or if they truly are experiencing it as time goes by (despite time being weird in that place!). As Mortis teaches, the light side is creation, the dark side is destruction. The son represents the natural destruction, essential to life and the universe. So when the Father warns about him falling to the dark side, it may sound weird for mortal ears, but actually means, he should not overstep his role and cause more destruction than balance would attest him in the natural cycle of everything. So the Mortis arc literally uses the term "Dark Side" for two different meanings, just like fandom does, to illustrate the misunderstanding that is at the core of all dark side problems. The natural dark side/destruction is a part of balance, the unnatural overstepping Dark Side that causes imbalance though is not. The problem thus is this, the point of view: If you look at it from the pov that the light is creation and the dark is destruction, then the dark side is natural but overstepping its use makes it evil to a degree, yet not entirely as not all of it needs to be defeated but only the overstepping part of it corrected (something which the Lightsiders often mistunderstood and too heavily fought). If you look at it from the pov that the light side is all that is natural including destruction and creation, and that the dark side is all that is unnatural, thus imbalancing and overstepping this balance between creation and destruction, then the Dark Side is something to be defeated and eradicated to restore the balance that is the Light Side. As you see it is all in the nomenclature and definition issues and different people with different definitions talking about the same thing at the core. The first Mortis episode kinda is the "gods" calling Anakin to fulfill his destiny. Once that failed, the second changes their gamebook to "we need to show him the errors of their ways and decisionmaking" and a different act is up, hence the different definitions and much more human-like Ones and their roles somewhat shifted to the perspective of the Jedi visitors who did not get their cosmic meaning beforehand. It kinda rhymes with Yoda integrating his shadow self in the other arc. Only that where he integrated his angry side, the Force Priestess showed there are more emotions than just anger to master and integrate, more selfs than just the one he encountered, like all she is split between to proof a point.
They are simply extremely powerful force wielders. That alone has led others to believe them to be gods. The father is exceptionally powerful and has not transcended his physical form by the time of the TCW, but the Son and the Daughter have, hence their ability to transform into winged beasts. The Father is so powerful that he can control the Son and the Daughter even after they left their physical forms behind. The dagger is a weapon imbued with the force by the Father, hence its ability to kill those that have transcended a physical form. It is my belief that the Dagger of Mortis could also kill a force ghost. So "ascended mortals" is probably the best description.
I see them both as Celestials and Gods. Celestials are so beyond everything that for any mortals are loke gods, they shape galaxy so its look like look in present. We have also Mother imprisoned in Maw cluster and make everyone around who are touch by her a lost mind, which remind a little Lovecraft. It could be discussion about execution, but I like idea behind kt. That there are cosmic forces beyonnd imaginatiom.