I have a 2018 59G with a different floor plan but same issues as yours. I had a cracked left taillight lens and was able to access the mounting nuts on the left taillight by removing some trim and drawers on the left side. I am assuming you will need to remove some trim around the wardrobe to access the taillight as well. The one on the right side of my rig is covered by the bath. I have not had the pleasure of dealing with that yet.
If all else fails, you may have to remove the lens using a hairdryer (not a heat gun), a putty knife and a lot of patience. I did this with my cracked taillight as an experiment. Once the lens is removed, you could drill out the housing where the mounting studs are and use different hardware to reattach the taillight. However, this seems like a lot of work. I am confident there will be a better way to access the taillight without removing the bathroom walls.