Every one of these goddesses is somebody's little sister. Most of them are used to being picked on, but they know they're their parents' darlings. Nephthys is the youngest of five, but Nut loves spending the evenings with her lastborn child.
Younger than her Olympian sisters Hestia and Hera, Demeter is the quiet little sister. But she's plenty tough. Just ask Hades. She beats him up every year come spring, but instead of stealing his lunch money, she takes back his wife Persephone instead. It's not stealing, though. Persephone's her daughter. (She might be the younger sister, but she's not that young!)
This Greek goddess of Night is rarely seen. Most of the time, Nyx calls in sick and does her assignments from home in a cave in Tartarus. You'll have better luck going to visit her if you can find her in the shadows.
Sure, she's Frey's twin sister, but he was born first, and he never lets Freyja forget it. Both of them are constantly creating and using magic items to try to be best. It's like a Norse mad scientist's lab in their place, between Freyja's feathered cloak and cat-drawn chariot and Frey's self-battling sword and ship-in-a-pouch. Stay out of the way when they're working on their science fair assignments!