Currently, in KOTLC, it is unknown who Sophie's parents are we have some information on her parents, as in some people who they aren't and Sophie doesn't know them. Most theories include that Forkle was lying to Sophie, witch if your gonna make a theory is what it might have to go in. What if Sophie didn't meet them? How could they be tied in?
Let's take a step back, all the way to the book that started it all, KOTLC book 1. In that book, we meet Jensi who has long been forgotten and irrelevant. Jensi is an amazing character and shouldn't be forgotten, but what if his family is more important to the series then we think? It has been theorized that Blur is Jensi's brother, which I believe is true it would make sense. One thing kinda bugs me about that theory, what is the long explanation that he would tell the main crew?
What if Jensi's brother knows one of her parents? That could be his motivation for joining the Black Swan. What if one day he is digging through one of his parent's stuff and he finds something about how they are apart of creating the project Moonlark, by donating his DNA to be the mother/father of her. He decided to join the group so he could learn about Sophie, his half-sister.
Jensi would most likely to be back as Sophie's brother and will cease to be irrelevant. Sophie could have gotten the enhancing gene from one of Jensi's parents because one could have the ability and we don't know about it. They also could look like Sophie and Jensi gets his looks from the other parent. Whether it would be Jensi's mom or dad is impossible to tell since we don't know anything about them.
Let's look at Sophie's other possible parent. We know that discovering Sophie's parents is world tumbling and Jensi's mom/dad isn't world toppling so if the theory is true that means tying the other parent in, so who could they be? Think about this what could topple the elven world not much right?
What do the elves strongly believe in? Light is more powerful than darkness. How could that tie into Sophie's parents, that wouldn't work? That animals should be allowed to live freely, but again that wouldn't work. I almost gave up at this point, what would topple the seemingly perfect elves world?
Elves know that they are better than humans in every way and they are proud of it, but what if they aren't? Elves have pretty week minds when you think about guilt, humans don't have as weak of minds. A lot of humans feel guilt every day and our minds don't break. What if humans are stronger and better then the elves in different ways that kinda make us more powerful but we can't access our "inner powers". What if they used a human to make Sophie so powerful.
I doubt it would look good to their world if humans were better in any way. It could lead to everyone to stop trusting the counsel and not listen to them. I don't think that the Black Swan would like this to happen and could keep them from telling Sophie her parents. The elves reaction could even be what ends the little peace they still have.
Could we pin it to a specific human? Well, the only adult humans we know of is Sophie's human parents and Mr. Sweeny. The problem is Sophie knows both of them! Well is there any human that knows about elves that were mentioned in the series. What if it was the human who lives in the house with a green door.
At the end of Flashback Sophie was deemed unmatchable, presumably because her parents are unknown and they have no way of knowing who they are. That would prompt Sophie to go out and learn who her parents are. We know that they will be in London because of the background of the cover. The house with the green door is in London too what if they gave Sophie the address of the house because that was her parent and she found out about them.
The human would know about elves (presumably from being recruited by the Neverseen) and could have given some DNA to make Sophie. What if the Neverseen tried to recruit them because they were the parent if our Moonlark, and could give him some information?
Sorry, this was super long, and if it made no sense :/. Welp thanks for finishing it.