Siblings names are:
[name_f][/name_f][name_f]Milena[/name_f] (Lena)
[name_f][/name_f][name_m]Nikolai[/name_m] (Niko)
[name_f][/name_f][name_f]Aurelia[/name_f] (Rori)
[name_f][/name_f][name_f]Rosalia[/name_f] (Rosy)
[name_f][/name_f]Our last name starts with a Z and ends with a very polish “ski” 
How about:
[name_f][/name_f][name_f]Anastasia[/name_f]
[name_f][/name_f][name_f]Theodora[/name_f]
[name_f][/name_f][name_f]Cressida[/name_f]
[name_f][/name_f][name_f]Delphina[/name_f]
[name_f][/name_f][name_f]Liliana[/name_f]
[name_f][/name_f][name_f]Tatiana[/name_f]
[name_f][/name_f][name_f]Paloma[/name_f]
[name_f][/name_f][name_f]Lydia[/name_f]
[name_f][/name_f][name_f]Irina[/name_f]
[name_f][/name_f][name_f]Isadora[/name_f]
[name_f][/name_f][name_f]Seraphina[/name_f]
[name_f][/name_f][name_f]Camilla[/name_f]
[name_m]Otto[/name_m]
[name_f][/name_f][name_m]Hugo[/name_m]
[name_f][/name_f][name_m]Felix[/name_m]
[name_f][/name_f][name_m]Dimitri[/name_m]
[name_f][/name_f][name_m]Xavier[/name_m]
[name_f][/name_f][name_m]Rafael[/name_m]
[name_f][/name_f][name_m]Lucian[/name_m]
[name_f][/name_f][name_m]Rupert[/name_m]
[name_f][/name_f][name_m]Benedict[/name_m]
[name_f][/name_f][name_m]Sebastian[/name_m] (my fave)
[name_f][/name_f][name_m]Leopold[/name_m]
Evangelina “Evie” would also be fab - and continue the L theme
Maybe you would like:
[name_f][/name_f][name_m]Danilo[/name_m] (Danny, [name_m]Dan[/name_m], [name_m]Nils[/name_m], Nilo)
[name_f][/name_f][name_m]Bruno[/name_m]
[name_f][/name_f][name_m]Rafael[/name_m] / [name_m]Raphael[/name_m] (Rafa, [name_m]Raffy[/name_m], Raph)
[name_f][/name_f][name_m]Andrei[/name_m] / [name_m]Andres[/name_m] / [name_m]Andreas[/name_m] (Andy)
[name_f][/name_f][name_m]August[/name_m] (Auggie, Gus)
[name_f][/name_f][name_m]Maxim[/name_m] / [name_m]Maximilian[/name_m] (Max)
[name_f][/name_f][name_m]Julian[/name_m] (Jules, [name_m]Jay[/name_m], Ian)
[name_f][/name_f][name_m]Cyrus[/name_m] (Cy)
[name_f][/name_f][name_m]Marcel[/name_m] / [name_m]Marcelo[/name_m] (Mars, Marc)
[name_f][/name_f][name_m]Leonid[/name_m] / [name_m]Leon[/name_m] / [name_m]Leonard[/name_m] / [name_m]Lionel[/name_m] (Leo)
[name_f][/name_f][name_m]Lorenzo[/name_m] (Enzo)
[name_f][/name_f][name_m]Emilian[/name_m] (Emil, Ian)
[name_f][/name_f][name_m]Anton[/name_m] (Tony)
[name_f][/name_f][name_m]Valentin[/name_m] (Val, Len)
[name_f][/name_f][name_m]Gabriel[/name_m] (Gabe)
[name_f][/name_f][name_m]Casper[/name_m] / [name_m]Kasper[/name_m] (Cas)
[name_f][/name_f][name_m]Fabian[/name_m] (Ian)
[name_f][/name_f][name_m]Roman[/name_m] (Rome)
[name_f][/name_f][name_m]Eduard[/name_m] (Ed, [name_m]Eddie[/name_m], Ned)
[name_f][/name_f][name_m]Elias[/name_m] (Eli)
[name_f][/name_f][name_m]Oscar[/name_m] / [name_m]Oskar[/name_m] (Ozzy)
[name_f]Adriana[/name_f] (Ada, [name_f]Adri[/name_f], Ana)
[name_f][/name_f][name_f]Antonina[/name_f] (Nina, [name_f]Toni[/name_f], Annie)
[name_f][/name_f][name_f]Emilia[/name_f] / [name_f]Emiliana[/name_f] (Emi, [name_f]Mila[/name_f], [name_f]Millie[/name_f], Mimi)
[name_f][/name_f][name_f]Amalia[/name_f] (Amy, [name_f]Mali[/name_f], Mila)
[name_f][/name_f][name_f]Marina[/name_f] (Mari, [name_f]Mar[/name_f], Mimi)
[name_f][/name_f][name_f]Marcella[/name_f] (Mari, [name_f]Mar[/name_f], [name_f]Marcie[/name_f], Ella)
[name_f][/name_f][name_f]Valeria[/name_f] (Val)
[name_f][/name_f][name_f]Valentina[/name_f] (Val, [name_f]Nina[/name_f], Tina)
[name_f][/name_f][name_f]Simona[/name_f] (Mona, Simi)
[name_f][/name_f][name_f]Alessia[/name_f] (Ally)
[name_f][/name_f][name_f]Camila[/name_f] / [name_f]Kamila[/name_f] (Cam, [name_f]Cami[/name_f], [name_f]Mila[/name_f], [name_f]Millie[/name_f], Mimi)
[name_f][/name_f][name_f]Angelica[/name_f] (Annie, [name_f]Angie[/name_f], Angel)
[name_f][/name_f][name_f]Eleonora[/name_f] (Ellie, [name_f]Ella[/name_f], [name_f]Lea[/name_f], Nora)
[name_f][/name_f][name_f]Natalia[/name_f] (Nat, [name_f]Talia[/name_f], Tali)
[name_f][/name_f][name_f]Evelina[/name_f] (Eve, Evie)
[name_f][/name_f][name_f]Adelina[/name_f] (Ada, [name_f]Addie[/name_f], Adele)
[name_f][/name_f][name_f]Luciana[/name_f] (Lucy, [name_f]Lucia[/name_f], [name_f]Lulu[/name_f], Lu)
[name_f][/name_f][name_f]Viviana[/name_f] (Viv, [name_f]Vivi[/name_f], Ana)
[name_f][/name_f][name_f]Violetta[/name_f] (Vivi, [name_f]Violet[/name_f], [name_f]Lettie[/name_f], Etta)
[name_f][/name_f][name_f]Karina[/name_f] (Kari)
[name_f][/name_f][name_f]Sabina[/name_f] (Bee)
[name_f][/name_f][name_f]Martina[/name_f] (Mari, [name_f]Martie[/name_f], [name_f]Tina[/name_f], Mina)
[name_f][/name_f][name_f]Cecilia[/name_f] (Cece, [name_f]Celia[/name_f], Celie)
[name_f][/name_f][name_f]Silvia[/name_f] (Silvy)
[name_f][/name_f][name_f]Estella[/name_f] (Stella, Esty/Estie)
For girls, maybe:
[name_f][/name_f][name_f]Georgianna[/name_f] nn “Gia, [name_f]Gianna[/name_f], Georgie”
[name_f][/name_f][name_f]Marietta[/name_f] (unsure if you want to avoid repeating initials) nn [name_f]Mari[/name_f], [name_f]Etta[/name_f], [name_f]Etti[/name_f], [name_m]Ari[/name_m]
[name_f][/name_f][name_f]Bianca[/name_f] nn “Bia, Bebe”
[name_f][/name_f][name_f]Vanessa[/name_f] nn [name_f]Essa[/name_f], [name_f]Essie[/name_f], [name_f]Nessa[/name_f]
[name_f][/name_f]For boys, maybe:
[name_f][/name_f][name_m]Brennan[/name_m] nn [name_f]Bren[/name_f]
[name_f][/name_f][name_m]Julian[/name_m] nn [name_m]Jules[/name_m]
[name_f][/name_f][name_m]Tavian[/name_m] nn [name_m]Tav[/name_m], [name_m]Tavi[/name_m]
[name_f][/name_f][name_m]Vincent[/name_m] nn [name_m]Vince[/name_m], [name_m]Vinny[/name_m]
[name_f][/name_f][name_m]Leopold[/name_m] nn [name_m]Leo[/name_m]
[name_f][/name_f]Hopefully these help!
[name_f]Milena[/name_f], [name_m]Nikolai[/name_m], [name_f]Aurelia[/name_f], [name_f]Rosalia[/name_f] and…
[name_f][/name_f][name_f]Lavinia[/name_f] (Vinni, [name_f]Livi[/name_f], [name_f]Liv[/name_f], Nia)
[name_f][/name_f][name_f]Anastasia[/name_f] (Taisie, [name_f]Ana[/name_f], Annie)
[name_f][/name_f][name_f]Cassandra[/name_f] (Cassie, [name_m]Sandy[/name_m], Andra)
[name_f][/name_f][name_f]Tabitha[/name_f] (Tabby, [name_f]Tiggy[/name_f], Tibby)
[name_f][/name_f][name_f]Frederika[/name_f] (Freda, [name_f]Rika[/name_f], [name_m]Freddie[/name_m], Fi)
[name_f][/name_f][name_f]Arabella[/name_f] (Belle, [name_f]Ara[/name_f], [name_f]Bella[/name_f], Bea)
[name_f][/name_f][name_f]Isadora[/name_f] (Dora, [name_f]Izzy[/name_f], [name_f]Isa[/name_f], [name_f]Sadie[/name_f], Ida)
[name_f][/name_f][name_f]Ingrid[/name_f] (Indie, Iggie)
[name_f][/name_f][name_f]Estella[/name_f] (Stella, Essie)
[name_f][/name_f][name_f]Tatiana[/name_f] (Tati, [name_f]Tiana[/name_f], [name_f]Tia[/name_f], Tana)
[name_f][/name_f][name_f]Larissa[/name_f] (Lissy, [name_f]Issy[/name_f], Lara)
[name_f][/name_f][name_f]Emilia[/name_f] (Emmy, [name_f]Mila[/name_f], Millie)
[name_f][/name_f][name_f]Nadia[/name_f] (Nia)
[name_f][/name_f][name_f]Juliana[/name_f] (Jules, Junie)
[name_f][/name_f][name_f]Eloisa[/name_f] (Ellie, [name_f]Elsie[/name_f], Lola)
[name_f][/name_f][name_f]Antonia[/name_f] (Ana, [name_f]Annie[/name_f], Nia)
[name_f][/name_f][name_f]Olympia[/name_f] (Pia, [name_f]Pippa[/name_f], [name_m]Oli[/name_m], Imy)
[name_f][/name_f][name_f]Marcela[/name_f] (Marcy, [name_f]Ella[/name_f], Mari)
[name_f][/name_f][name_f]Luciana[/name_f] (Lucy, [name_f]Lula[/name_f], Ana)
[name_f][/name_f][name_f]Noemi[/name_f] (Noa, Emi)
[name_f][/name_f][name_m]Konrad[/name_m] / [name_m]Conrad[/name_m] (Cord, Rad)
[name_f][/name_f][name_m]Emanuel[/name_m] (Manu, Ell)
[name_f][/name_f][name_m]Emilian[/name_m] (Emil, Milan)
[name_f][/name_f][name_m]Frederick[/name_m] (Freddy, [name_m]Rex[/name_m], Ricky)
[name_f][/name_f][name_m]Sebastian[/name_m] (Baz, Sebby, [name_m]Seb[/name_m], Bastian)
[name_f][/name_f][name_m]Caspian[/name_m] (Cass, [name_m]Ian[/name_m], Kip)
[name_f][/name_f][name_m]Lucian[/name_m] (Luca)
[name_f][/name_f][name_m]Gabriel[/name_m] (Gabe)
[name_f][/name_f][name_m]Tobias[/name_m] (Toby, [name_m]Tai[/name_m] / Ty)
[name_f][/name_f][name_m]Rafael[/name_m] (Rafi, [name_m]Rafe[/name_m], Rafa)
[name_f][/name_f][name_m]Benedict[/name_m] (Ned, [name_m]Benny[/name_m], [name_m]Ben[/name_m], Beck)
[name_f][/name_f][name_m]Dorian[/name_m] (Dan, [name_m]Danny[/name_m], Ian)
[name_f][/name_f][name_m]Julian[/name_m] (Jules, Jude)
Thank you! I never even considered the L theme, but now I agree it needs to be continued! I also feel committed to the two syllable, 4 letter nicknames at this point 
[name_f][/name_f] So many rules I have accidentally imposed on myself.
Thank you! You actually recommended a few family names I hadn’t considered.
Thank you so much!
Thank so much for these suggestions! So many beautiful names
[name_f]Luciana[/name_f] (Lulu) or [name_m]Dimitri[/name_m]
[name_f]Daniela[/name_f] nn [name_f]Dani[/name_f] or [name_f]Ella[/name_f]
[name_f][/name_f][name_m]Leonidas[/name_m] nn [name_m]Leon[/name_m]
[name_f][/name_f][name_m]Alden[/name_m] nn [name_m]Aldo[/name_m]
[name_f][/name_f][name_f]Valentina[/name_f] nn [name_f]Tina[/name_f]
[name_f][/name_f][name_m]Alexander[/name_m] nn [name_m]Alex[/name_m]
[name_f][/name_f][name_f]Everly[/name_f] nn [name_m]Ever[/name_m]
[name_f][/name_f][name_f]Julietta[/name_f] nn [name_f]Etta[/name_f]
[name_f][/name_f][name_f]Cleopatra[/name_f] nn [name_f]Cleo[/name_f]
[name_f][/name_f][name_f]Delilah[/name_f] nn [name_f]Lila[/name_f]
[name_f][/name_f][name_f]Dolores[/name_f] nn [name_f]Lola[/name_f]
[name_f][/name_f][name_f]Elizabeth[/name_f] nn [name_f]Lisa[/name_f]
[name_f][/name_f][name_f]Alexandra[/name_f] nn [name_m]Alex[/name_m]
[name_f][/name_f][name_f]Luciana[/name_f] nn [name_f]Lucy[/name_f]
[name_f][/name_f][name_m]William[/name_m] nn [name_m]Liam[/name_m]