Okay, read through this for the first time and I have to wonder why they are acting like children so much yet they keep on claiming that they are older internally. They aren't acting like reasonable adults at all. Some of it you can attribute to the abuse and the fact that they died as high school students not mature adults, but their ability to jump to conclusions and inability to communicate even the most basic of concerns is unbelievably frustrating for people who are suppose to be "grown ups on the inside".
What's more is they are horribly inconsistent... well Arien is at least. Arjen hasn't even been developed as a character at this point. He's mostly inconsequential. As for the inconsistent part, they don't believe anything anyone else has to say. they instantly doubt everything that has been said to them by their family. Instantly doubt the maids. You don't even trust the brother who you know is risking his life to protect you with a magic barrier, but they trust the words of Rosea instantly. A guy they have only meet twice. Why? Because he read it out of a book? Did you even think about confirming the contents of the book?
Again I could forgive some of these things if the characters in question were just abused children without any wold experience, but the author keeps bringing up their past life without giving any details other than they died "for reasons unknown". Were they abused in their past life as well? We don't know. It's never clarified. You have to assume so from their behavior. Even then it still doesn't explain why they instantly trust the words of a person they don't know over the person they know is sacrificing some of his life energy to protect them. "Yes they are just putting themselves in a compromising position where they feel ill and have to sleep all for their own amusement. Indeed, this must be the case".