
At most an attempt would happen and if it does, the brother would be like “you can take everything else from me but not her.” Cue fighting. Cyr defeating the villain and everyone lives happily ever after.
The manhwa is called the Cheerful Countess Sisters. And the tone of the manhwa doesn’t indicate anything too heavy. There’s a drama tag but drama can range from those gut wrenching reads of torture and rape to “I like him but I saw him talking to another woman which hurt me in the feefees.”

It might be that the situation is similar but since the people are different and they've learned from their parent's mistakes they'll change their ways. I feel their actions would be how the previous parent's affair would have turned out if they worked it out, so like an alternative ending of what could have been.
Honestly no one is born evil and in the flashback we saw that the brothers were very close until an incident. As of now we don't know what happened so I'm not gonna generalize against him. The sisters also had misunderstandings between them but they turned out to be the best of friends so maybe the author is trying to parallel that with the princes. Maybe they'll become brothers again like them and rekindle their relationship.
The ML doesn't want to be king plus it's tiresome being queen with so many traitorous eyes around you. Charlotte has had enough trouble in her childhood, she doesn't need that atmosphere to heal her psychological issues. They both simply want a relaxing life free of troubles.
So my hypothesis on the ending would be. The king falls in love, they fight over her, someone acts out of the previous fate and tries to communicate, they get along, the king leaves them alone, charlotte and the red head marry so they are both duke and duchess of her estate. Something along those lines but there could be wild cards, who knows.

Oh yea both the sisters and the brothers have been led around by their parent's squabbles and affairs in the past so if they were able to look past their parent's crimes and think for themselves then they would truly make a life for themselves without the influence of their nasty parents. That's a lot of symbolism going into it. The sisters have already addressed it and now it might be the pair of brothers' turn. That would be a meaningful ending for the unfortunate children who were branded with their parents' crimes.
So we found both of the MLs of the series!!!!!!!!!! Omg let the sisters swap identities pls and thx. Char dresses like Kara and meets red head boi and the fall in love.