
Can someone explain the three brothers situation? From what I know, eldest and "youngest" is not blood related? Who are full and halfbrothers with ML?

Ml and older brother are blood related, they have the same parents. When they were younger mls dad brought younger brother to the house saying "he will be your younger brother". In reality , younger brother is the son of mls dad's crush or first love. After his first love and her husband got into a accident or something and died, he brought younger brother to them. The younger brother has a special condition where his blood doesn't stop whenever he gets a small scratch. So when the dad brought younger brother to the house, mls mother didn't like that and argues with the dad (obviously) ( they always argue, every single time). While they were arguing, the younger brother accident got hurt and the blood didn't stop coming out. So the older brother said he will take responsibility of the younger brother and took younger brother with him. And after 10 or so years, they got freaky with eachother, that's the start of "spilled blood"

So yeah, the older brother and younger brother are not blood related. In the "spilled blood" manhwa they really got freaky with eachother. The older brother was supposed to be a father like figure to the younger brother. When they were doing the shakalaka the younger brother even called the older brother "appa" !!???
Because the older brother asked him to call that otherwise he wouldn't fuck him(??). So ml and older brother are related and older brother and "younger brother" are in a relationship (??)

I have read the whole novel and people who consider this a love story (even if the author herself thinks this), are completely delusional.
Leila will not go to college and decide to become a town teacher to Matthias' delight because this means they're together in Arvis. Matthias makes sponsorships to various things including the Leila's school so he has an excuse to encounter her. He "torments" Leila by keeping this gentleman facade to others when he visits the school but makes advances towards her and when she refuses, he pours ink on her.
Uncle Bill will make a massive mistake with an explosion on the mansion garden (something to do with the new electrical work which he was being stubborn about) completely annihilating the precious plants. He was meant to go to prison so Matthias makes this a blackmail to Leila. He will not send Uncle Bill to prison and continue to hire him as long as he can restore the garden... if Leila becomes his whore/mistress.
Leila desperately agrees and Matthias takes her immediately on the floor. Once he's finished, he leaves Leila on the cold floor. This rapey sessions continue with Leila sometimes fighting back because the engagement with Claudine (and Claudine seems to have caught on their physical relationship), is making her guilty as a mistress. Matthias traps her again by blackmailing that he will tell Uncle Bill how Leila has whored herself to him if she decides to end things.
When Kyle gets back for a vacation, he catches Matthias raping Leila again in the cottage, but to save face, Leila tells "I love you" to Matthias to convince Kyle she's in love with Matthias so that he thinks she's not a whore. Kyle does not believe this and gets angry with Leila anyway.
To cut many scenes short, the mistress thing will get spread over Arvis and inevitably reach Uncle Bill. He quickly understands how Leila sold herself for his sake and blames himself. So, he decides to run away with Leila to the other country. By now, Leila has gotten pregnant but they do not address this. Matthias tries to get her back but Claudine,his mother and grandmother prevent him.
Leila and Uncle Bill lives for a short while in this new country but war begins (between the country they escaped to and Matthias' country). Matthias holds a high position in the military and has discovered that Leila and Uncle Bill has been in this country so he secretly was on a mission to track them down while participating in the war. Long story short, bombing by Matthias' country to where they was, killed Uncle Bill and Leila finally calls him "father" on his death bed. Because of the chaos, and feeling lost already Leila decides to go to the sea and die. Matthias finds her with her swollen belly and kidnaps her into the military base. He "nurses" Leila back into health but when she refuses, he blackmails her again that he would kill Kyle(who is also enlisted) in this war. When Matthias realizes Kyle was the only card left, he forces Kyle to be the one to take care of Leila because he knows she won't resist Kyle.
When the war was in a dire moment, Matthias was suddenly urgently needed and he had to part ways with Leila. Leila magically realizes she is "in love" with Matthias and asks him to return to her. (the war was ending with Matthias' country was already winning so i dont get this arc)
Leila returns to Arvis quietly and gives birth to a son, Felix who is the spitting image of Matthias. She prays for Matthias return oh so romantically in the newspaper hoping he's not on the death list. So basically, Matthias fakes his death for a while which sends the Duchy into disarray. This devastation for his mother and grandmother about his "death" was him setting up a "less bad" devastation that he is going to marry Leila, a commoner.
So he marries Leila and Leila can go to college now.
Leila is loveydovey with Matthias as if she wasnt just trapped into wanting to have a family with him now that she lost Uncle Bill. And they have another child who is blond.
(Reading the side stories with Leila and Matthias' marriage is so disconnected with the messed up dynamic they first had and the problems they didn't even resolve)

I read the novel too but I don't recall some of the things you've said. I did some digging and apparently there are some misleading fan translations going around to spark controversy and that Yonder (the website I used to read this on and has the official translation) is the genuine one. Here's the reddit post: https://www.reddit.com/r/MaleYandere/s/iNpJejqmHn.
But still, I do not condone what Matthias did to Leyla is any way. He still treated her like shit and SAd her.

Sorry, wrong link lol: https://www.reddit.com/r/MaleYandere/s/m9hlGozFui
I feel like Taeha has something to do with Mincheol's debt and that's how he got interested in NaHaesoo.
Can the ruse pls end now that she's seen him suited up rich? The mystery has gone for too long and yet there seems to be a new revelation every now and then... First Taeha's father, then Lee Jay's woman, and now, Mincheol's connections? CAN TAEHA'S MOTIVATIONS BE REVEALED NOW?!