How exciting!
I would go:
Marion & Ruby
Imogen & Cora
Marguerite & Adelaide
Cordelia & Evelyn
Mary & Thea
And for some ideas with middles:
Marianne Blanche & Cora Dorothy
Mary-Faye Joanna & Tabitha Ray Cora
Mix and match!
*wouldn’t go Joanna as a first name when you have a Josephine - too close! Josie/Joey/Jo etc.
Ideally, all would have own starting letter / sound.