There are 2 diffs and a transfer case. The transfer case needs special fluid and you should only use the oem fluid on the transfer case. It’s basically a wet clutch pack.
Front diff, I haven’t looked at but is a super pain in the ass to get to the fill plug. Or it was at least on my 4.8i with adaptive drive. Bmw routed the adaptive drive hydrolic lines in front of the fill port. There is a special set of shorty Allen wrench’s you’ll need.
The rear diff is limited slip so it would need friction modifiers correct? Redline or equivalent 75w-85 is recommended for the front, no after market fluids available for the Xfer case. Rear needs friction modifiers.
https://www.ecstuning.com/BMW-E70-X5.../Differential/
I’d tend to stick with oem fluid for the rear diff, as they have been known to be noisey without the oem fluid.