We like classic, but not too common names. British feel is a bonus.
I personally love Sasha and Maya, but can't use them due to a niece and a dog having them! DH has suggested Leila, but i think that's increasingly common. Do Americans know how to pronounce Cosima?
The children all have/will have middle name similar to Hutchins and last name similar to Barr, so no "G" names to avoid initials GHB, but otherwise most names seem to work.
Re: Little sister for Simon?
Imogen
Arabella
Matilda
Lydia
Adaline
Beatrice
Hermione
Georgette
Clementine
Florence
Cecilia
Philomena
Cosette
Nadia
Nadine
Louisa
Francine
Francesca
Lydia
Iris
Daphne
Cordelia
Poppy
Ella
Lily
Daisy
Phoebe
Freya
Thea
Lucy
Luna
Ruby
Matilda
Willow
Penelope
Beatrice