I have a very old save that I kept for years doing new content but I wonder if there is a way to change paths for Irinlia now, still talking about her, I never managed to trigger the tentacle scene to happen, could someone explain that to me too ?
There's indeed two path for Irinlia now, the 'bad' one requiring to send her to your dungeon, the 'good' one to give her to the guards (and then visit her to the prison and freeing her).
For the tentacles scene, you must have chosen the 'bad' path for Irinlia as well as Lace, and have cleared the hard (or advanced, I'm not sure) level of the Spire of Courage in Begus. Then, talk to the guard at the bottom floor of your dungeon, he will give you the quest to take some spore and grow the tentacles. Then I think you must talk to Lace to trigger the scene.
No, I don't think you can change either Lace or Irinlia paths, and as far as I know, this scene requires both of them. Though, the scene should still be unlocked in the CG room if you've finished their good paths.
EDIT: yeah I checked my save, with the good path for both, the bad path scenes are unlocked in the CG room.