See, I wish the manhwa is smart enough to realize this. But it's not. It's not intelligent enough for that. If they had portrayed the twins while giving out an excellent example like this on why they're acting the way they did, I wouldn't have dropped it. But I've been burned so many times by mangas where their MCs act stupid, readers defend them with logical reasonings, manga continues having them acting stupid, ends the story, leaving readers out to dry and scoffs at all kinds of explanations readers gave before. In the end, all sides lost, the ones who hated MC, and the ones who defended them.
Torture regresses the mind. That is a fact. Memories of the past fade over time while making new ones, that is also a fact doesn't matter if those memories are from the same or another life. In case of the latter they might just be even fainter from the start. Being reborn into a completely different world already shakes people up enough. But afterwards the twins didn't even get time to take a breather and settle down instead they got tortured from the beginning for five whole fucking years. So in their case remembering their last life is a disadvantage since they'll always clearly remember those abhorrent years while a normal child wouldn't at least conciously remember most of the first 6 years of their life. On the other hand all in all it's a wonder their mind didn't completely regress to that of children or become mentally disabled! Having each other, the mental, telepathic connection and the memories of their past life helped to prevent the worst as it seems. A curse and a blessing at the same time those memories are...
I really hope Riolu can let go of the past and his current affiliations and become someone loyal only to the twins! Maybe help them find all bastard children and take them in to make sure none of them have to suffer the way the three of them did anymore.