Hello! I have the answer for you here, copied from the devblog:
Will the characters being gender selectable make it easier to figure out who they are?
You can only romance one gender in each playthrough. Choosing Edith will make all the ROs female, and choosing Edward will make them all male.
It is unfortunate, but I had to do it this way to preserve the mystery. I’m sorry, fellow pan/bi people. There are always multiple playthroughs!