I like Ivy and Declan a lot! Etta is cute, not really my style but it's pleasant and unexpected. It would be cute as a nn for Bernadette or Harriet/Henrietta.
I really love the idea of Declan, Ivy, and Stella. Stella goes so well with your style and your subset. Has sort of a magic to it like Ivy does but without being matchy or too nature-y.
Ivy and Declan are good together.
My favorite of your current choices is Lila.
First of all, I really love the names Ivy Ramona and Declan Thomas. Good job momma!
For a sister to Ivy and Declan, I think Lila Violet is rather darling.
I also like these names...
I see Eliza for you. To me, Ivy is a name that is stylish and pretty, but it has a bit of a sharp edge. Ivy is smart, witty, and maybe she enjoys emo music or indie movies with sad endings. Eliza has all those components for me too. Smart and pretty, but just different enough.
Also: Hazel, Elena, Lucia, Vivian
Etta will always be Etta James to me.
I adore your kids' names. I just might cry happy tears if you name their little sister Fiona.
If that's too matchy with Declan, my next suggestion is Leona.
I have a brother Declan :)
If this helps, if my youngest brother was a girl, he was going to be named Delaney Maeve. I think it works nicely with Declan!
If it helps, Ivy and Declan are two of my top names for future siblings to our daughter NORA. :)