If I'm reading the map right, it's really hard to get to room #18/19 and talk with Yome, Yoshi or fight Jacole. To get to room 19 you either need 1. a piece of the Second Sun, 2. a way to dispell or bypass the magic lock on the door in room #4, or 3. Go through both the Mausoleum and the Cartographer dungeons.
From my reading of rooms #3 and #15, It doesn't sound like the party can move through that space without a daylight spell. My party doesn't have that or Dispell making getting the geese virtually impossible till they get through most of the dungeon. It also sounds like rooms #15 and #16 are caves made/inhabited by Milkshake, and that makes room #17 and #18 really strange since that means they don't have a direct access to any other part of the Palace.
I think the easiest thing todo is change the description of #15 so it is passable but Lirion cannot be reached without a piece of the Second Sun. This would make all of the Garden accessible without relying on a specific spell. Also the text for rooms #18 and #19 is confusing. It's not clear if the fight with Jacole is meant to be in room #18 or #19 and #19 is labeled 'Backstage' and 'Auditorium' and #18 being 'Backstage'