Since your other boys name have a 2/2 and 1/1 syllable flow. I kind of like the idea of your third having a 3/3. So running with that I’d suggest…
[name_f][/name_f][name_m]Finnegan[/name_m] nn [name_m]Finn[/name_m]
[name_f][/name_f][name_m]Remington[/name_m] nn [name_f]Remi[/name_f]
[name_f][/name_f][name_m]Atticus[/name_m] nn [name_m]Kit[/name_m]
[name_f][/name_f][name_m]Gideon[/name_m] nn Gid or [name_m]Denny[/name_m]
[name_f][/name_f][name_m]Sullivan[/name_m] nn [name_m]Sully[/name_m] or [name_m]Van[/name_m]
[name_f][/name_f][name_m]Everett[/name_m] nn Rett
[name_f]Annabelle[/name_f] nn [name_f]Annie[/name_f] or [name_f]Belle[/name_f]
[name_f][/name_f][name_f]Josephine[/name_f] nn Joe/ Josie/ Posy/ [name_f]Sophie[/name_f]
[name_f][/name_f][name_f]Delilah[/name_f] nn [name_f]Lila[/name_f]
[name_f][/name_f][name_f]Virginia[/name_f] nn [name_f]Ginny[/name_f]
[name_f][/name_f][name_f]Susannah[/name_f] nn [name_f]Sue[/name_f] / Susy/ Sanni/ [name_f]Suki[/name_f]
[name_f][/name_f][name_f]Luella[/name_f] nn [name_f]Lu[/name_f] or [name_f]Ella[/name_f]
[name_f][/name_f][name_f]Jessamine[/name_f] nn [name_f]Jessie[/name_f] / Jess/ Sammy/ [name_f]Mina[/name_f]
[name_f][/name_f][name_f]Adelaide[/name_f] nn Addie/ Lady/ [name_f]Della[/name_f]
[name_f][/name_f][name_f]Cecilia[/name_f] nn [name_f]Cece[/name_f]
[name_f][/name_f][name_f]Rosanna[/name_f] nn [name_f]Rose[/name_f] / [name_f]Anna[/name_f]