I love the names you have for your kids! They all fit so well together. I think [name_u]Arthur[/name_u] or [name_f]Alice[/name_f] from your list would fit nicely. [name_f]Nora[/name_f] is also cute.
Some suggestions…
[name_m]Louis[/name_m], [name_f]Margot[/name_f], [name_u]Henry[/name_u], and [name_f]Noelle[/name_f]
[name_m]Louis[/name_m], [name_f]Margot[/name_f], [name_u]Henry[/name_u], and [name_f]Naomi[/name_f]
[name_m]Louis[/name_m], [name_f]Margot[/name_f], [name_u]Henry[/name_u], and [name_u]Wren[/name_u]
[name_m]Louis[/name_m], [name_f]Margot[/name_f], [name_u]Henry[/name_u], and [name_f]Willa[/name_f]
[name_m]Louis[/name_m], [name_f]Margot[/name_f], [name_u]Henry[/name_u], and [name_f]Ophelia[/name_f]
[name_m]Louis[/name_m], [name_f]Margot[/name_f], [name_u]Henry[/name_u], and [name_f]Delilah[/name_f]
[name_m]Louis[/name_m], [name_f]Margot[/name_f], [name_u]Henry[/name_u], and [name_f]Ivy[/name_f]
[name_m]Louis[/name_m], [name_f]Margot[/name_f], [name_u]Henry[/name_u], and [name_f]Jane[/name_f]
[name_m]Louis[/name_m], [name_f]Margot[/name_f], [name_u]Henry[/name_u], and [name_u]Haven[/name_u]
[name_m]Louis[/name_m], [name_f]Margot[/name_f], [name_u]Henry[/name_u], and [name_f]Cordelia[/name_f]
[name_m]Louis[/name_m], [name_f]Margot[/name_f], [name_u]Henry[/name_u], and [name_u]Jack[/name_u]
[name_m]Louis[/name_m], [name_f]Margot[/name_f], [name_u]Henry[/name_u], and [name_u]Rhys[/name_u]
[name_m]Louis[/name_m], [name_f]Margot[/name_f], [name_u]Henry[/name_u], and [name_u]Scott[/name_u]
[name_m]Louis[/name_m], [name_f]Margot[/name_f], [name_u]Henry[/name_u], and [name_m]Casper[/name_m]
[name_m]Louis[/name_m], [name_f]Margot[/name_f], [name_u]Henry[/name_u], and [name_u]Luca[/name_u]
[name_m]Louis[/name_m], [name_f]Margot[/name_f], [name_u]Henry[/name_u], and [name_m]Zane[/name_m]
[name_m]Louis[/name_m], [name_f]Margot[/name_f], [name_u]Henry[/name_u], and [name_m]Frederick[/name_m]
[name_m]Louis[/name_m], [name_f]Margot[/name_f], [name_u]Henry[/name_u], and [name_u]Franklin[/name_u]
[name_m]Louis[/name_m], [name_f]Margot[/name_f], [name_u]Henry[/name_u], and [name_m]Gregory[/name_m]