I know an Arabella. She is always referred to as Bella.

Axel is a rockstar name to me so Delta just doesnt seem edgy enough to stand up next to it. The name that came to me when I thought about a Sister for your DS was Kat. When I think of a brother's name, the weirest name came to my mind John-Paul, JP for short. I know you didn't ask for my opinion so please feel free to disrefard my left-field response.