
I replied this to someone but i'm posting it again so you guys don't miss it. This is what I understand so far it could be wrong in some places so feel free to correct me. Hope this helps.
I'll write a short one first then. If you want to know more details scroll down.
Shorter version.
Seolhyun (the hyung) is naturally a female lycan. But thinks he's a male lycan cause ino brainwashed him to think so. His heat came and he got pregnant with 3 kids. 2 of them are directly blood related to hwa and are twins. The third one is a mystery. We don't know what it is. All 3 of them are in danger of dying. Lee bin doesn't care about their death.
Longer version.
Seolhyun is the child of ino's siblings... So I'm guessing genetically there's a problem with him that is causing a threat to his kid's lives. In the past something traumatic happened between seolhyun and hwa to the point where lee bin and ino decided to wipe their memories away. Seolhyun still remembers a little. But hwa does not. While wiping away seolhyun's memories he made him think that he's a male lycan even though he was a female... This ended up dividing his personality. The seolhyun we know is timid, not confident about his feelings and thinks he's a male.. But the other personality remembers what happened in the past and this part of seolhyun is fully aware of him being a female, which is constantly trying to take over. It sees hwa as a threat. Thats why seolhyun tried to hurt hwa but the blood thingy called idea sprung up to hwa's defence. But it couldn't do anything as it recognised hwa's blood in seolhyun (his babies). As ordered by his creator (lee bin) it must protect those who are of his blood, his kin. It report this back to lee bin and who then further decides to investigate the matter as he doesn't want seolhyun to hurt hwa. For him atm, hwa is more important than his kids. As stated by others there's an error with translation. The characters used kin instead of grandchildren which was then translated into son. Lee bin most definitely cares for hwa but as a vampire his emotions doesn't extend to anyone else other than his close family members, especially with seolhyun as he probably caused or was a part of something that hurt hwa in the past. So he's kind of cold to him..
Any other detail that you wish for me to clarify comment down below. I'll get back to you. This is what I remember so far.

I'm glad I've found someone that understood the same way I did.
But about all of them being in danger of dying. Do you think that it has to do with the species they belong too?
Since Hwagok in season 1 almost died while giving birth, due to Hwa's blood getting into contact with his (he was a lycan at the time). So, if even one of the babies is a vampire, the risk is higher, as they are all together in the same place.
Plus, we don't know what effects might Seol mutant side might have on those babies?
What do you think?

I agree.. The possibility of the third one being a vampire or having part vampire genes is pretty high. That could also explain why they aren't considered triplets.. Because maybe one is genetically totally different from the rest. But we can only conjecture atm. The future chapter will tell. I'm super excited to see them all. ε=ε=(ノ≧∇≦)ノ

I liked someone's suggestion on the mystery child being Seolhyun female Lycan trying to be born cause Idea said it different and isn't blood so it's not related to Hwa and I think Idea would know if it was a vampire plus the chances of the babies being a vampire are low since Seolhyun is Lycan and Hwa is half of each. Idea also said they're in danger and Seolhyun female Lycan is very assertive and wants to be the host/dominant personality.
I also feel like Lee Bin not caring about his grandchildren is more from his own experience and all the drama that came when Hwa was born; I think he thinks it would be better if they weren't born plus I feel like the story of Seolhyun and Hwa when they were younger will come up soon so I also think that's another reason for Lee's coldness towards the situation. Either way, I can't wait to see the twins and mystery baby cause the fever is growing strong! but that would also mean this manga will come to an end when that happens ┗( T﹏T )┛

Doesn't seem like anyone's interested in knowing what jeong is feeling whatsoever. You're in a relationship for 8 years. When you confessed the other party's response was... Okay we can try... Just coz we've been friends for so long why not... No clear i love you too and yes I'd love to date you.. You're obviously are going to feel insecure all the time.. That's normal... Lack of communication is a major issue.. But not just because of jeong alone.. Try imagining yourself in a relationship where you never once felt loved. Where you never once felt needed... Instead you felt like you were a burden on your partner. That psychologically damages you on many levels. I'm not saying kangwoo didn't love him.. He had his own form of love for jeong... But his love wasn't enough to keep jeong happy.. There are time when one partner feels like they're giving more to the relationship and not receiving as much... If you're not happy in a relationship i dont see why you have to continue being with them...
I'm no relationship expert but i can tell what's wrong with their relationship... Kangwoo was never once vocal about his relationship.. He never once showed affection in public.. He always felt scared of anyone finding out... Does anyone realise how jeong must've felt... What I can gather from this comment section is that... Everyone just hates jeong.
Did he move on too quick yes.. He should have given himself more time to heal.. But when you've gotten out of a relationship where you were unhappy af... And suddenly there's this person who makes you feel everything you've wanted from a relationship its hard to pass.
Gyutae isn't all for sex either... I can tell. He liked him.. But if someone doesn't really love you but wants to just use you for sex... You do become a bit salty.. His fault was actually having sex with him right away.. He should've waited.. Comforted him.. Made jeong fall in love with him.. Right now. Jeong feels happy with gyutae only because he's getting what he wants and the painful memories from his relationship with kangwoo seems to be fading..
I have not read the raws i don't know how this ends.. But i do understand what the author is trying to tell.
Sorry for this.. I just felt too bad for jeong after reading the comments. Felt the need to defend the poor bastard. Lol ╮( ̄▽ ̄)╭

I get all of this and you’re right but for a relationship that’s lasted for 8 years the development and lack of communication is just ridiculous and unbelievable. For the sake of the plot sure. But this isn’t believable in the slightest that a 8 year would be tossed out the window with never once expressing insecurities present in their relationship. Let alone to give not even a hint of an explanation, and begin sleeping with your ex’s superior. If you even knew someone capable of this stupidity and passive aggressiveness I’d say you were better off without them to begin with.
I WANT TO MUTILATE THAT BASTARD THAT TRIED TO HURT THE KITTEN... HE GOT OFF WAY TOO EASY... (╬ ̄皿 ̄)凸