I've updated the pic. The filler at the front (orange circle) does the front diff, and feeds through a tube behind the torque converter to also do the bearing for the output shaft on the other side.
The filler at the rear (red circle) does the Torsen centre diff.
The rear diff filler is on the side here:
Yes, they are all 75/90. I recommend Castrol Syntrans for changes but if you're just topping up pretty much anything that grade will do.
Its rare for the rear diff to leak much except at very high mileages. They're usually a little damp around the output flanges but anything worse than than is unusual. That would be unlikely to make its way to the exhaust too.