Idk if u can count the years after they were reincarnated cause they were babies so if their mental age when they died was18 or smthg it kinda makes sense cause the way they think and speak is pretty mature, plus they live in a different world now so they're obviously not gonna be that smart cause the world works differently. Also if they weren't reincarnated they wouldn't have been able to communicate so flawlessly and help each other through their trauma.
Why does some people always think that poking at someone's typographical error is fun? Well not that I can say much since I've said negative stuff about this work. The twins aren't using their brain properly to be honest though, the fact that they don't trust their father and siblings shows a lot since they were abandonedand ignored in the beginning and also being abused by their bitch mother, which means trusting a stranger should be also hard for them. I've read novels, manga, webtoons etc for a decade. I know what story should be logical or just-for-fun read one.

This is one of the shittiest story. Like what the others said, there's no point in the reincarnation setting, they dont even have the brain to act like a proper young teen what more is that they're shown to have a mental age of 23-25. Like fuck no, they're so fucking dumb