Hello! [name_f]My[/name_f] husband and I are pretty sure we’re going to name baby girl number 2 Celine/Selene, we just can’t decide with spelling/origin/meaning we want to go with (they’re both gorgeous 
). We also don’t really have any idea for middle names to pair with Celine/Selene because all the names we’ve previously liked sound really choppy when paired with her, unfortunately.
She is joining big sister [name_f]Flora[/name_f] [name_u]Camille[/name_u] and our surname begins with P!
I adore [name_f]Celine[/name_f] - so pretty and sleek!
I’d suggest the middles:
[name_f]Celine[/name_f] [name_f]Poppy[/name_f]
[name_f]Celine[/name_f] [name_f]Primrose[/name_f]
[name_f]Celine[/name_f] [name_f]Violet[/name_f]
[name_f]Celine[/name_f] [name_f]Anya[/name_f]
[name_f]Celine[/name_f] [name_u]Ruby[/name_u]
[name_f]Celine[/name_f] [name_u]Ivy[/name_u]
[name_f]Celine[/name_f] [name_f]Iris[/name_f]
[name_f]Celine[/name_f] [name_u]Juniper[/name_u]
[name_f]Celine[/name_f] [name_f]Adele[/name_f]
[name_f]Celine[/name_f] [name_u]Esme[/name_u]
I love [name_f]Celine[/name_f] - so pretty!
such a pretty name and sounds so nice with flora!! i prefer selene, but celine is beautiful too. celine makes me think of the singer! 
I like [name_f]Selene[/name_f] better, just because it’s more visually different than [name_u]Camille[/name_u]. [name_f]Beautiful[/name_f] name!
Middle ideas:
[name_f]Selene[/name_f] [name_f]Adela[/name_f]
[name_f]Selene[/name_f] [name_f]Alisa[/name_f]
[name_f]Selene[/name_f] [name_u]Aubrey[/name_u]
[name_f]Selene[/name_f] [name_f]Breanna[/name_f]
[name_f]Selene[/name_f] [name_f]Dalia[/name_f]
[name_f]Selene[/name_f] [name_u]Elia[/name_u]
[name_f]Selene[/name_f] [name_f]Emelyn[/name_f]
[name_f]Selene[/name_f] [name_f]Ines[/name_f]
[name_f]Selene[/name_f] [name_f]Julissa[/name_f]
[name_f]Selene[/name_f] [name_f]Kassandra[/name_f]
[name_f]Selene[/name_f] [name_f]Layla[/name_f]
[name_f]Selene[/name_f] [name_f]Lea[/name_f]
[name_f]Selene[/name_f] [name_f]Melia[/name_f]
[name_f]Selene[/name_f] [name_u]Michell[/name_u]
[name_f]Selene[/name_f] [name_f]Riana[/name_f]
[name_f]Selene[/name_f] [name_f]Rosalia[/name_f]
[name_f]Selene[/name_f] [name_f]Viviana[/name_f]
[name_f]Selene[/name_f] [name_f]Vivianna[/name_f]
I’d use Seline. Celine makes me think of Celine Dion instantly.
Selene Jessamine
Seline Larissa
Seline Alicia
Seline Eleanor
Seline Catherine
Seline Rosalind or Seline Rosamund
Seline Elestren
Seline Estella
I would say Celine as it’s a more tailored, Frenchy look to me to match Flora Camille - but I can see the pp’s point that it is visually close to Camille - not that it really matters as it’s a middle but they do look alike.
To me, Celine is sleek and stylish, and Selene is warmer, friendlier and more fun. My normal preference is Celine and it’s possible you’ll get a few pronunciation issues with Selene.
Some middles (all with Celine but some suit the Selene spelling better):
Celine Hazel
Celine Violet
Celine Estelle
Celine Julia
Celine Harlow
Celine Tessa
Celine Elisabeth
Celine Mabel
Celine Daphne
Celine Lucy
Celine Pearl
Celine Amelie
Celine Iris
Celine Elsa
Celine Ivy
Celine Charlotte
Celine Bridget
Celine Yarrow
Celine Beatrice /ix
Celine Marigold
Take or leave: a related name you might like which I think goes a bit better with Flora and is more equitable across the sisters is 
Celeste (Celine is a variation of Celeste).