In this chapter, we learn that the two vampire siblings have made up, and that they've pretended to be enemies in order to hide their true identities from each other. In other words, they're making up to each other, and they don't want each other to know about it. They're pretending to be family, but they can't hide anything from their family, so they have to do whatever they want with each other's secrets. This is a big deal, and it's clear that the vampire siblings are trying to trap their sister in a trap.