What makes things doubly difficult, is the nuts are octagonal not hexagonal like a "normal" nut. So sockets just won't cut it. The only thing that fits is a 3/4" open ended spanner, with all it's limitations. Add that to the "monkey metal" the spindles are made of and it's a recipe for disaster.
Sometimes the things come undone easily (not often) occasionally they will yield to persistence, take the dash out and hold the back of the spindle firmly with a large water pump pliers, douse everything in penetrating fluid and pray. If this fails, cutting the nuts off is the only last resort.
But it's worth doing, leaks here are almost totally responsible for rot in the box section under the screen that the top of the column and brake pedal box mounts on! It's a lot easier to stop the leak than fix rust in this complicated and hard to access compound curved panel, not to mention the damage done as the water makes it's way down the car, rusting A pillars, inner sills and floor pans on it's way and ruining carpets. All for the sake of a few pennorth of sealer. And maybe a couple of nuts.
On a secondary note, if you've had a leak for a long time and you suspect the spindles, it's probably worth pulling the dash out (the whole lot, crash pad and all) and inspecting the box section for rust. Most of it is invisible with the crash pad in place and the rot can fester unnoticed for years. Been there, done that, got a drawer full of T shirts!
Oh the dash went ages ago and the panels have already rotted. I have welded in new metal in each corner inside and outside. Part of the leak was the scuttle panel which had rotten but that is now all new metal.
Yet water is still getting in, so the next thing to eliminate is the spindles.