According to some spoilers...
Swan is just basically that one kid who got lucky and touched That locket with magic first (instead of Lilyan and it's for her protection) and absorbed its power changing her appearance.
So Swan and Lilyan are not related at all.
It also grants her a few years of life rather than her dying that next day she's left on that orphanage. So as soon as that magic depleted she dies.
the pendant has divine powers meant to protect the real daughter. the pendant also gives the child the black hair blue eyes appearance. swan isn't the real daughter, she happened to touch the pendant as a baby and she was meant to die early but the pendant gave her a few years of life until the power ran out. MC is the real daughter. also, her eyes are turning greener and hair is getting darker
So Swan that we saw in early chapters is not her original appearance? I see
I thought Swan n mc are twin cause of fantasy genre. The kidnaper probably used magic to make everyone forgot. But it looks like I'm wrong (〜￣△￣)〜