@lola They're not related by blood and the adoption was only on paper to protect him as a child. He never even lived with them. Thalia and Aegis grew up more like siblings than Loina and Yen.
Spoiler!
All in all, Loina, the og fl, and Yen, the og ml, get together in the end. One of the few things that actually stay the same as the og. They fall in love at near first sight when they meet later on in the story, at least loina does as far as I remember.