For the tranny, I find it easiest to remove the LH floorboard. I've got a funnel with a hose that is about 14" long. This gets inserted into the fill hole, hold the funnel and fill that with 90wt. For the transfer case, I'll pull the center seat cover and do the same thing from there. I'll only use those squeezy bottles for the swivel housings and the diffs...they are just too fiddly to fill the tranny...
I bought a proper Gear Oil Gun. It looks like a regular grease gun but has no pump handle. In effect, it is a big seringe. Suck about a 3/4 quart of oil into the thing then push it back out the hose by pushing the handle back in. Works best if you stick the hose in the tranny fill hole first mind you.
I use a pump that mounts on top of a 5-gallon bucket. I've tried a lot of ways over the last few decades, and this is the best device I have found. Second best is a pressurized garden sprayer. Or you can use a hose on the squeezy bottle and fill from inside the vehicle by removing the cover under the middle seat.