Congrats!
I like the name Maisie and if Goldie is Goldie all the time, it does follow the two syllable -ie pattern. If she gets Marigold and possibly anyway, I am not sure I would have another M name and it could be a little close to both of the other two girl names as a sort of smoosh of Marigold and Elsie. Marigold Louise could even be Maisie for short. But this has to balanced by the fact that we live our lives not as sibling sets so if Maisie is the fave, keep it!
Here are some other options:
Junia Camille
Iris Josephine
Tabitha Violet “Tabby”, “Tibby”
Sylvie Rosanna / Beatrice
Clementine Pearl
Bridget Helena “Birdie”
Tallulah Catherine
Tess Magnolia
Lydia Frances
Phoebe Caroline
Verity Lenora
Imogen Clara
Hope some of these appeal! 