I don’t like any of your names, sorry. I slightly favour your ABC names: [name_u]Auden[/name_u], [name_f]Brielle[/name_f], and [name_u]Connelly[/name_u].
If it were me I’d go with:
[name_f]Miranda[/name_f], [name_u]Morgan[/name_u], and [name_f]Maybelle[/name_f]
or
[name_f]Aurora[/name_f], [name_f]Beatrice[/name_f], and [name_f]Celestine[/name_f]
[name_f]Elodie[/name_f], Everlynn & Eliss: I like [name_f]Elodie[/name_f] a lot, but I don’t like Everlynn or Eliss much at all. [name_f]Elodie[/name_f], [name_u]Evelyn[/name_u] & [name_f]Elise[/name_f] would be (and fit together) much better in my opinion.
[name_u]Auden[/name_u], [name_f]Brielle[/name_f] & [name_u]Connelly[/name_u]: I’m not a fan of any of these; the first and last sound so very masculine/surname-y.
[name_f]My[/name_f] sets within the guidelines would be:
[name_f]Ariadne[/name_f], [name_f]Antheia[/name_f] & [name_f]Aviva[/name_f]
[name_f]Ariadne[/name_f], Briseis & [name_f]Calliope[/name_f]
Same letter:
[name_f]Felicity[/name_f]
[name_f]Flora[/name_f]
[name_f]Frances[/name_f] ([name_u]Fran[/name_u])
Or
[name_f]Carys[/name_f]
[name_f]Clara[/name_f]
[name_f]Corinne[/name_f]
ABC:
[name_f]Alla[/name_f]
[name_f]Bethany[/name_f]
[name_f]Carys[/name_f]
[name_f]Anastasia[/name_f]
[name_f]Belinda[/name_f]
[name_f]Corinne[/name_f]
[name_f]My[/name_f] sets in the guidelines would be:
[name_f]Elizabeth[/name_f] ([name_f]Lizzie[/name_f])
[name_f]Eleanor[/name_f] ([name_f]Nora[/name_f])
[name_f]Evangeline[/name_f] ([name_f]Evie[/name_f])
or
[name_f]Adelaide[/name_f] ([name_f]Ada[/name_f])
[name_f]Audrey[/name_f] ([name_f]Addie[/name_f])
[name_f]Anastasia[/name_f] ([name_f]Ana[/name_f])
I don’t like any “B” names so I can’t do the ABC names.
Same letter:
[name_f]Eleanor[/name_f] “Nora”
[name_f]Emilia[/name_f] “Mila”
[name_f]Eliza[/name_f] “Ellie”
or
[name_f]Emmeline[/name_f] “Emme”
[name_f]Eleonora[/name_f] “Ellie”
[name_f]Evangeline[/name_f] “Evie”
or
[name_f]Livia[/name_f] “Livy”
[name_f]Leonor[/name_f] “Leo”
[name_f]Lucy[/name_f] (or [name_f]Lyra[/name_f])
Alphapetical:
[name_f]Alba[/name_f]
[name_f]Bali[/name_f]
[name_f]Clara[/name_f]
or
[name_f]Clementine[/name_f] “Emmy”
[name_f]Desiree[/name_f] “Daisy”
[name_f]Elise[/name_f] “Lily”
or
[name_f]Katharina[/name_f] “Katie”
[name_f]Livia[/name_f] “Livy”
[name_f]Matilda[/name_f] “Mattie”
Same Letter:
[name_f]Maple[/name_f] [name_f]Beatrix[/name_f]
[name_f]Mariela[/name_f] [name_f]Pearl[/name_f]
[name_f]Mavis[/name_f] [name_f]Clementine[/name_f]
They’re not really “in sync” with each other but I picked them because of how they’re connected to me. 
ABC:
[name_f]Aurora[/name_f]
[name_f]Beatrice[/name_f]
[name_f]Charlotte[/name_f]
For triplets with the same starting letter: [name_f]Esther[/name_f], [name_f]Eleanor[/name_f] and [name_f]Elspeth[/name_f]
For ABC triplets: [name_f]Amelia[/name_f], [name_f]Bethany[/name_f] and [name_f]Clara[/name_f]
I wouldn’t really want matchy names for triplets so they would probably be:
[name_f]Melody[/name_f], [name_f]Aurora[/name_f] and [name_f]Hazel[/name_f]
Or
[name_f]Esther[/name_f], [name_f]Leona[/name_f] and [name_f]Adele[/name_f]
I love [name_f]Elodie[/name_f]. I like [name_u]Ever[/name_u] but not Everlynn. [name_u]Ellis[/name_u] is cool and fits with [name_u]Auden[/name_u] and [name_u]Connolly[/name_u] (also cool names) but not with the other E’s. [name_f]Brielle[/name_f] doesn’t fit with [name_u]Auden[/name_u] and [name_u]Connolly[/name_u]'s surname style.
For me…
Same letters: [name_f]Cecily[/name_f] & [name_f]Cosette[/name_f] & [name_f]Cassia[/name_f]
ABC: [name_f]Astrid[/name_f] & [name_f]Briar[/name_f] & [name_f]Coralie[/name_f]
Kind of matchy word name (slightly gp) sets I’d love: [name_f]Cameo[/name_f] & [name_u]Story[/name_u] & [name_f]Briar[/name_f] or [name_f]Nova[/name_f] & [name_f]Lyra[/name_f] & [name_u]Vega[/name_u]
I prefer your ABC choices!
Mine would be:
ABC:
[name_f]Agnes[/name_f]
[name_f]Beatrix[/name_f]
[name_f]Clara[/name_f]
Same letter:
[name_f]Esther[/name_f], [name_f]Emma[/name_f], [name_f]Eve[/name_f]
[name_f]Cecily[/name_f], [name_f]Clara[/name_f], [name_f]Chloe[/name_f]
Same letter: all A’s because I have a lot of A favorites!
[name_f]Amaryllis[/name_f] [name_f]Joy[/name_f] “[name_f]Lilly[/name_f]”
[name_f]Arcadia[/name_f] [name_f]Rosalie[/name_f] “[name_f]Cady[/name_f]”
[name_f]Anastasia[/name_f] [name_f]Liv[/name_f] “[name_u]Sasha[/name_u]”
Different letters: i would prob use the same number of syllables. (It’s a fetish of mine)
[name_f]Olympia[/name_f] [name_u]Ruby[/name_u] “[name_f]Mia[/name_f]”
[name_f]Arcadia[/name_f] [name_f]Rosalie[/name_f] “[name_f]Cady[/name_f]”
[name_f]Elysia[/name_f] [name_u]Phoenix[/name_u] “[name_f]Ellie[/name_f]”
(bonus: all have paradisian/heaven connections)
Same Letter: [name_u]Connelly[/name_u] ([name_f]Elle[/name_f] or [name_u]Connie[/name_u]), [name_f]Clara[/name_f], [name_f]Charlotte[/name_f]
[name_f]Florence[/name_f], [name_f]Fleur[/name_f], [name_u]Finley[/name_u]
A,B,C: [name_f]Adelaide[/name_f], [name_f]Brighton[/name_f], [name_f]Clara[/name_f]
Same Letters:
A, B, C Method:
I prefer the same letter method 
Without the matching letters I’d have [name_f]Charlotte[/name_f] [name_f]Louise[/name_f], [name_f]Elizabeth[/name_f] [name_f]Claire[/name_f], and [name_f]Rose[/name_f] [name_f]Caroline[/name_f].
Same letter: [name_f]Elizabeth[/name_f], [name_f]Eleanor[/name_f], and [name_f]Elora[/name_f].
Alphabetical order: [name_f]Caroline[/name_f], [name_f]Daisy[/name_f], and [name_f]Elizabeth[/name_f].
I would chose the ABC over doing all the same letter to help give them more individuality!
For me personally, I would chose:
[name_f]Aria[/name_f], [name_u]Brooklyn[/name_u], and [name_f]Claire[/name_f]
Same Letter:
[name_f]Miranda[/name_f], [name_f]Matilda[/name_f], [name_f]Melina[/name_f]
[name_f]Susanna[/name_f], [name_f]Samantha[/name_f], [name_f]Serena[/name_f]
[name_f]Rosalie[/name_f], [name_f]Rachel[/name_f], [name_f]Ramona[/name_f]
A, B, C:
[name_f]Asha[/name_f], [name_f]Brynn[/name_f], [name_f]Claire[/name_f]
[name_u]Allison[/name_u], [name_f]Bridgette[/name_f], [name_f]Cassandra[/name_f]
[name_f]Annika[/name_f], [name_f]Britta[/name_f], [name_f]Cassia[/name_f]
[name_f]Annora[/name_f], [name_f]Brielle[/name_f], [name_f]Cecily[/name_f]
M:
[name_f]Maisie[/name_f], [name_f]Matilda[/name_f] & [name_f]Molly[/name_f]
E:
[name_u]Evelyn[/name_u] “[name_f]Evie[/name_f]”, [name_f]Emily[/name_f] & [name_f]Eliza[/name_f]
ABC:
[name_f]Annabel[/name_f], [name_f]Beatrice[/name_f], [name_f]Clara[/name_f] - Easiest
[name_f]Sylvie[/name_f] [name_f]Anneliese[/name_f]
[name_f]Stella[/name_f] [name_f]Annabelle[/name_f]
[name_f]Sabine[/name_f] [name_f]Noelle[/name_f]
[name_f]Annabel[/name_f] [name_u]Meredith[/name_u]
[name_f]Briony[/name_f] [name_f]Sabine[/name_f]
[name_f]Clara[/name_f] [name_f]Emmeline[/name_f]
For the same letter I would do:
For ABC’s I would choose:
[name_f]Emma[/name_f]
[name_f]Eloise[/name_f]
[name_f]Eliza[/name_f]
[name_f]Anna[/name_f]
[name_f]Brynn[/name_f] ?
[name_f]Claire[/name_f]
[name_f]Annabel[/name_f], [name_f]Alice[/name_f] & [name_f]Amelia[/name_f]?
[name_f]Aurora[/name_f], [name_f]Belle[/name_f] & [name_f]Clementine[/name_f]?
I definitely couldn’t name children this way…