My older daughter’s name is [name_f]Delphine[/name_f] and I’m pregnant with our second and likely final baby. We are team green, but are settled on [name_m]Frederick[/name_m] for a boy. For a girl we had nothing that was feeling right and then I re-remembered [name_f]Celeste[/name_f] which we had strongly considered for [name_f]Delphine[/name_f]’s name. Miraculously my husband loves it and wants it to be the one (we have argued endlessly over girls names). I had sort of taken it out of contention And didn’t bring it up earlier in the decision process because of the [name_u]Del[/name_u] and Cel similarity. [name_f]Delphine[/name_f]’s nickname is [name_u]Del[/name_u], but we would plan to use [name_f]Cece[/name_f] as a nickname if we use [name_f]Celeste[/name_f]. [name_f]Do[/name_f] you think the el at the start of both names makes them too similar or am I reading too much into this?
I don’t think they’re too similar! If you were planning to call [name_f]Celeste[/name_f] ‘Cel’, then it would be too similar, but since you plan to use [name_f]Cece[/name_f] (which I love, by the way!) then I think they work just fine together. [name_f]Delphine[/name_f] and [name_f]Celeste[/name_f] are lovely sister names, and I adore [name_m]Frederick[/name_m] too!
I actually like the symmetry, without the names being too close!
They sound great together, not too similar at all!
Delphine and [name_f]Celeste[/name_f] are not too close – the syllables don’t actually work out to be [name_u]Del[/name_u] and Cel (as OP wrote). [name_u]Del[/name_u]-feen and Seh/Suh-lest. The L in [name_f]Celeste[/name_f] falls on the second syllable, not the first.
Cece isn’t my personal style, but it is fine as a NN. There are also NN options playing off of the L in CeLeste’s name, like [name_f]Letty[/name_f] perhaps.
Delphine and [name_f]Celeste[/name_f] make for perfect sister names! I adore your naming sense!
I didn’t even notice the the start of the full names being similar until you pointed it out, and since there’s no emphasis on it in the nicknames either, I think you’re completely fine.
I love love love Cel And [name_u]Del[/name_u] 
I think they work fine as sister names.
I don’t think there’s a problem with these 2. In fact they are lovely as sisters. [name_f]Cece[/name_f] makes a great nn for [name_f]Celeste[/name_f]. The Cel part of [name_f]Celeste[/name_f] is pronounced more as “Seuh” so that differentiates it from [name_f]Delphine[/name_f] too. If you didn’t use [name_f]Cece[/name_f] then [name_f]Esty[/name_f], [name_f]Essie[/name_f], [name_f]Cissy[/name_f] or [name_f]Tess[/name_f] would be preferable over Cel.
My thoughts exactly! I don’t pronounce [name_f]Celeste[/name_f] with a sel sound, it’s like what penelope_lynson described (seh-lest) unlike [name_f]Delphine[/name_f]. If you don’t even plan on using Cel as a nickname, definitely go for it. [name_f]Delphine[/name_f] and [name_f]Celeste[/name_f] are beautiful together.
Not too similar for siblings! I think [name_f]Delphine[/name_f] and [name_f]Celeste[/name_f] is a terrific set.
Not at all! [name_m]Frederick[/name_m] and [name_f]Celeste[/name_f] are lovely!
No, I really think it isn’t too close. You should totally use it!
I don’t think they’re too similar! They feel well matched 
I think they work perfectly together! Not too similar, but both magical and charmingly vintage. I don’t find the sounds to be too similar at all.
Delphine and [name_f]Celeste[/name_f] make a lovely sister pair.
Nope. I didn’t even realize the similarity until you pointed it out.
Not too close at all! Love how they’re both French! And love the nn [name_f]Cece[/name_f]