The FNs are all going to be what I chose for my ultimate sibling set a few days ago, because I love how they go together, even though they are boring.
Katherine Rose -- "Kate" or "Katie" depending on her personality and preference.
Elizabeth Anna -- I think I'd like to use Betty or Beth as her nickname, but it would depend on her preference.
William Henry -- I would definitely call him Will, because I don't care for the other nicknames.
Theodore James -- I prefer Teddy to Theo, so that's what I'd want to call him, but Teddy feels childish, in my opinion.
I would've used Jane in a middle name spot for one of the girls, but it's too similar to James and I knew I was using that for one of the boys. The MNs I ended up using for the girls are the middle names of my sisters, so that's honoring. And, for a bonus, Anna and Elizabeth are my cousin's names, so I'm honoring them as well. Anna is also a family name. William is my grandfather's name, so I wouldn't mind using it in real life. I don't have any relatives named Henry, Theodore, or James, but I think they work well with this set. In real life, if I were to do this set, I'd make Theodore's middle name Francis, because that honors two family members, Frank and Frances, and that way each of the kids would have at least one honoring name.