You'll need something like this for the transfer case and rear differential:
https://www.fcpeuro.com/products/bmw...-euro-b3300000
Along with a fluid extractor of your choice, FCP Euro sells one also. You need it to get down into the unit since you have to pull fluid from the fill hole.
Not sure how much comes out of the rear differential, but you'll get about 50% of the fluid out of the transfer case using this method. None of the fluids are lifetime. There's many reports out there of strange shudders during acceleration that stop when changing these fluids, particularly the transfer case. So obviously something is worn out.
They're a little time consuming, but not hard to do. Even the transfer case, daunting as it may seem, is not terribly difficult. Just support the case with a floor jack, remove the support bracket, and you have access to the fill hole.