
I have to wonder if he liked her before they were married? His feelings seem to be very intense for a woman that he’s only spent one night with so I’m just wondering if there’s any backstory?

Spoiler.. read this if you really want to know
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He used to work under a blacksmith that works for Duke Croix. It was near the Duke's mansion and so he met Maxi when they were young(maxi- 6; riftan-12) and had some interactions with each. Since then when faced with hardship (he really did had a cruel life before becoming a renowed Knight) he would always think about Maxi so you would say at a young age he already has his heart set on loving Maxi ε=ε=(ノ≧∇≦)ノ

Honestly I don’t think the red haired guy is going to cause any drama (at least I hope not because I’m already in love with him and it’s too late to stop me. I’ll be heartbroken if he’s bad).
We already have seen that he has a girlfriend (?), so I really don’t think he’s hitting on Bom, I just think he’s overly friendly (which is something our baby needs! #GiveHeabomFriends2020) which will cause unnecessary jealousy on Taesung’s behalf.
I’m more worried about the gossiping that has been foreshadowed. First we see his coworker gossip about the female coworker to Bom on his first day, then we see that same guy gossiping about both her and Bom to the Team Leader, and now the Team Leader/Red haired guy is cautioning Heabom against telling people his life because people gossip. I just hope their time at this work place won’t be too harsh on them!

I don’t get why the author made the other children look and behave like adults, why not just make them older?
The manifestation thing is just weird and unnecessary to me. Why do they need to turn into young adults/older teens as soon as they turn 3? And how come their mentality is also affected? Why couldn’t they just make the princes slightly older? I really don’t think it would affect the plot that much, and it’s not even like there aren’t siblings with a large age gap, heck, my older siblings are 14 and 16 years older than me.
The second prince is 10 years old yet he looks and acts like an adult, why not just make him 16? Also, if he’s 10 how old is the youngest? And if they manifest into an young adult appearance and not age until they turn 18, why does the 3rd brother look smaller and yonder than the 2nd prince? Aren’t they all just meant to look the same age until adulthood?
Sorry, that plot point just seems so unnecessary and I can’t seem to get over it.

I feel like they’re acting very immaturely. They’re mentally 25, yet they can’t seem to accept or understand anything other than what they want to hear. They keep whining about being abandoned and being treated like b*stards, and are not willing to understand anyone else’s points. It’s like they are actual children who can’t comprehend adult politics.
They’re mature when it suits the plot and immature when it suits the plot. Pick a side guys.
This is still okay and I’m going to see where it goes, but there are just SO MANY of these reincarnation family plots that this doesn’t feel unique. I wish they’d focus more on the twin and telepathy abilities.

You can be immature and mature at the same time. Your post is an example. Whining about how the characters don't act the way you expect. You can't take your own advice and see the twins point of view, either, thus earning your new title of hypocrite ٩(๑❛ᴗ❛๑)۶
[[Insert how old twins are]] years of physical, mental, emotional, and verbal abuse. No rehabilitation nor therapy to help reverse the damage. Of course they will only be looking to save themselves and constant believe someone has it out for them because hello— being in their "mentally 25 y.o." state does not make them immune to insults and years of abuse.
Whining about how they were abandoned? Yes, throw out every single-parent child's feelings in real life. Try to empathize with them. Their father abandoned them. A figure who, in their previous life, was supposed to help support the family along with the rest of its members. That figure bailed on them.
"OH but he had so many restrictions." Restrictions my ass. He is the most powerful man in the land. Probably wealthy too by the show of horses. He couldn't hire a spy, he couldn't hire a double maid, he couldn't have used a disguise to meet in person, he TOTALLY couldn't have asked a SINGLE person to help him out and find if his children were alive. If he was a parent who truly cared, he would have gone to the ends of the Earth to see if they were alive instead of simply assuming (which is an immature trait. Why aren't you calling the father out? He's probably like, 30 and he acts like a new teen father. Again, I don't blame him for doing so, but you're the one who wanted people to see things from many sides (=・ω・=)).
They're mature because they had many common experiences before coming to this world and have some background knowledge. Isolating yourself from the rest of society due to physical and emotional abuse is not a sign of immaturity, but a sign of damage that needs to be addressed and corrected soon, or else the mentality will be hard to change in the future.
For a story that’s called “Make me Bark” there’s surprisingly not much pet play