Degel: I know she can promote directly from Knight to Great Knight but I hate Knight, they're so slow (in both meannings). Moreover, i can reclass her right after her recruting (since she begin at level 10, if i remember well). About Discipline, If she max out soon, I can trow away Discipline instead of Defence+2
Selena: I agree with you with how low damage she'll done... It's pretty hard to find an utility for her since I have so many "Swordmaster": Lucina, Azure, Wood and Mark (in some way). But I'll for sure redone her.
Noire: As an archer, she is not supposed to get attacked. So Vengence and Miracle are just a security. But you're right, Vantage might be more useful, I'll perhaps exchange her father and Selena's... I'll think about it.
n_n: Honestly, I had forgot that Frederick have to be at level 10 before reclassing. So you're right I'll keep him as a Great Knight and pass down Luna.
EDIT:
There is the changement... I hope it's better!
Selena (Dark Knight)
Noire (Bride)
n_n (Manakete)