"I do not care. If you two want to further prove yourself, then you better accept this challenge." One of the main reasons why Arion is putting this kind of challenge to his kids is that he wants them to get to these kinds of tight situations.
In the world that they live in, tight situations mostly happen all the time. And if his kids are not used to it, then their lives could be at risk or someone else's life.
It is harsh, but for their sake, Arion has to give them limited choices or tight situations. 'They want to be part of the underworld? Then, they better be ready to face more of these challenges.' Arion inwardly said.
After thinking things through, Anna and Aaron fully understand what their father is trying to do. Truth to be told, they did not expect their father to train them. Rather than getting angry at their father's challenge, the twins are more up to it.