I’ve got a girls name list, and tend to lean towards multi-syllable feminine names which end in an ‘a’. However, if I had more daughters would it seem like too much together!
Some of the names on the current list are (and, yes, for some reason I love ‘a’ names):
[name_f]Angelina[/name_f]
[name_f]Antonella[/name_f]
[name_f]Olympia[/name_f]
[name_f]Amalia[/name_f]
I love long, flowy, multi-syllable girl names! They’re my favorite style. I don’t think it’s too much at all. 
Don’t think it’s too much at all! [name_m]Plenty[/name_m] of siblings have almost the same name, and these aren’t even that close.
I think they go great together and I can imagine nicknames that have more distinct sounds from each other so I wouldn’t be worried about the same sounds in the full name 
At first glance [name_f]Angelina[/name_f] & [name_f]Antonella[/name_f] are very similar but [name_f]Angie[/name_f] & [name_f]Nella[/name_f], totally different and equally adorable!
Oooooo these are incredible together! Like Pilar’s of feminine strength 🪻 
Some suggestions:
Giogiana
Narcisa
Soledad
Augustina
Giuseppina
Rafaella
I think the other sounds in the names are distinctive enough that they hold their own. Plus, -a is a common ending so it doesn’t feel over the top
They don’t feel like too much at all to me, I wouldn’t notice anything unusual about a sibling set like this! 4-syllable girl names aren’t at all uncommon. Other than [name_f]Angelina[/name_f] & [name_f]Antonella[/name_f] which are maybe too similar, I think all the names on your list could work really well as sisters.
Some ideas for long, feminine names without an -a ending:
[name_f]Amaryllis[/name_f]
[name_f]Adelaide[/name_f]
[name_f]Belphoebe[/name_f]
[name_f]Clementine[/name_f]
[name_f]Celestine[/name_f]
Clarimonde
[name_f]Emmeline[/name_f]
[name_f]Emilienne[/name_f]
[name_f]Elsinore[/name_f]
[name_f]Genevieve[/name_f]
[name_f]Guinevere[/name_f]
[name_f]Juliette[/name_f]
[name_f]Lavender[/name_f]
[name_f]Melusine[/name_f]
[name_f]Primrose[/name_f]
[name_f]Rosalind[/name_f]
[name_f]Rosamund[/name_f]
[name_f]Seraphine[/name_f]
[name_f]Vivienne[/name_f]
[name_f]Violette[/name_f]
[name_f]Zephyrine[/name_f]
[name_f]Olympia[/name_f] 
I love [name_f]Olympia[/name_f], I don’t really know why but I just love the sound of it!
I don’t think it’s strange at all, in fact I think they go very well together 
I’ve also been loving [name_f]Olympia[/name_f] recently- I don’t know why but it’s just been stuck in my mind!