[@Shadow Dragon] that's just because that's how their powers are but children of nyx don't have necromancer I'm pretty sure the just control shadows and I'll show you the list of things I allow that don't follow the books 

1.the shadows being used as a second home 
2. Demigods eyes changing from their powers 
3. Hosts making portals whenever and without a egyptian artifact present 
4. Certain things concerning powers energy wise and what they can do 
5. Enherji going from Valhalla to earth whenever 
6.other miscellaneous things