Juliette is my oldest's middle name. I think Ginevra would sound nice with your sibset.
But apologies you wanted more Celtic sounding names and not to keep with the more mainland Europe theme, my bad should have read the post properly.
For Scottish/Irish but with a good fit you would probably need to go for the easier to spell names rather than the super traditional.
Elspeth (nn Elsie)
Ignore since I didn't see the date the original post was posted lol