So, as of now in prologue you can have all of them gain at least a bit. Then in chapter 1 the main characters for gains are Rosalind, Emilia and Liora. You can also have the maid and Perlene put on a bit of pudge through not as much as the main characters.
Viewing post in Expanding Universe: A Filling Journey comments
Spoiler ahead:
Try telling Perlene you're looking forward to your next meeting.
As to the maid, there are two opportunities. One is for example to tell her that your walk with Rosalind was a little bit romantic. Then you have to be on Emilia's route. And when she asks you if you're in some kind of palace romance, ask her back if she wants to be included!