I was able to remove both shutters through the opening exposed by removing the rear glass. There are 6 screws on the front and 4 screws on the rear shade. You have to move the shades in steps to reveal the screws. Once all screws are undone you can slide the shades to free them from the side mountings. Not easy, but possible. Given the problem with your rear shade, this may not work for you.
Image is of location of rear glass mounting bolts. Says one use only, but I re-used them. I found with the glass in the vent position, access to the front bolts was easier. Torx 25 I'm sure.
There is extra info over on this link, but I only found that this morning, I didn't use it. Gives detail on how the rear and front shades interact. Mine were both functional so I was able to work with the cassette in the car.
Moonroof and/or Sun Shield remove and replace - Bimmerfest - BMW Forums