Oh Sadie Eloise is very pretty. I have to say I love Maeve from your signature. Otherwise, maybe, Audrey or Clara? As Sadie is a secret pleasure I mine, I think it goes beautifully with my kids names (Alice and Harry!).
I'm struggling with boys names at moment.....I think you need a spunky, slightly cheeky name. Am thinking of cheeky boys I know (apart from my Harry!), maybe Alexander (Zander), Asher or George.
What names have you thought of and discarded?
Sadie is currently on my list and it's actually one of my favorite names to make sibsets with! I think it goes with a lot of different styles, but works perfectly with other short, spunky, somewhat quirky girl names. The options for boys are literally endless style wise.
From your list I think Maeve and Lila fit the bill perfectly. Sadie and Anna would also be adorable! I see Hattie is on your list, but I think Hadley or Hallie fits better. Some other names that make me smile when placed next to Sadie:
For boys I really think anything goes, some of my favorites next to Sadie:
Simon (if you're ok with same letters. This sibset is adorable)
Mason (obvious difference in popularity, but Sadie and Mason is PERFECT)
I LOVE Sadie... and I really like all he names in your sig!
From there the best matches with Sadie are:
Some other suggestions:
Love the previous suggestions of Alice and Tessa for girls
Love previous suggestions of George and Cole for boys