Just.....Ew!

I'm really enjoying Masquerade by Melissa De La Cruz. However, there is one aspect that is just extremely hard to get past. Mimi and Jack Force (twins in "this cycle") are brother and sister. But they are vampires and haved lived many lifetimes. According to the story, they were bonded (husband/wife type bond) forever. So each cycle they come back as a couple so to speak. So the fact that they are brother and sister but have feelings for each other that are not sibling like is just kind of........well, ew.