Sister Name (HP Fanfic)

So, I’m attempting a [name_m]Harry[/name_m] [name_m]Potter[/name_m] fanfiction where I actually created the main characters of it instead of creating weird storylines for existing characters.
The main characters are the [name_m]Severin[/name_m] triplets (surname taken from a webtoon ‘Muted’), two of which I’ve named.

[name_f]Amalie[/name_f] [name_m]Severin[/name_m]
[name_f]Emmeline[/name_f] [name_m]Severin[/name_m]
??? [name_m]Severin[/name_m]

I need help for a sister name yet again, because I don’t know what I’m doing.
Also, house colours.

[name_f]Amalie[/name_f], [name_f]Emmeline[/name_f], and…
[name_f]Isabel[/name_f] / [name_f]Isabelle[/name_f] / [name_f]Isabela[/name_f] / [name_f]Isabella[/name_f]
[name_f]Isaline[/name_f] / [name_f]Isabeau[/name_f] / [name_f]Isadora[/name_f]
[name_f]Olivet[/name_f]
[name_f]Livia[/name_f]
[name_f]Lisette[/name_f]
[name_f]Imelda[/name_f]
[name_f]Ottilie[/name_f] / [name_f]Ottilia[/name_f]
[name_f]Ophelie[/name_f] / [name_f]Ophelia[/name_f]
[name_f]Penelope[/name_f]
[name_f]Umbrielle[/name_f]
[name_f]Imogen[/name_f]
[name_f]Lucille[/name_f] / [name_f]Lucia[/name_f]
[name_f]Lillian[/name_f] / [name_f]Liliana[/name_f]

[name_f]Amalie[/name_f], [name_f]Emmeline[/name_f], and…

[name_f]Estelle[/name_f]
[name_f]Celeste[/name_f]
[name_f]Seraphine[/name_f]
[name_f]Ophelie[/name_f]
[name_f]Melusine[/name_f]
[name_f]Yvette[/name_f] / [name_f]Yvonne[/name_f]
[name_f]Giselle[/name_f]
[name_f]Elaine[/name_f]
[name_f]Rosalie[/name_f] / [name_f]Rosella[/name_f]
[name_f]Odetta[/name_f]
[name_f]Madeleine[/name_f]
[name_f]Lucia[/name_f] / [name_f]Lucienne[/name_f]
[name_f]Fabienne[/name_f]
[name_f]Juliette[/name_f] / [name_f]Julienne[/name_f]
[name_f]Genevieve[/name_f]
[name_f]Delphine[/name_f]
[name_f]Apolline[/name_f]
[name_f]Cecily[/name_f] / [name_f]Cecilie[/name_f]
[name_f]Claudine[/name_f]
[name_f]Sylvie[/name_f]
[name_f]Aurelia[/name_f] / [name_f]Aurelie[/name_f]
[name_f]Camille[/name_f]
[name_f]Valerie[/name_f]
[name_f]Mirabelle[/name_f] / [name_f]Mirabeau[/name_f]