There is nothing to grease in the axle, unless you really fancy pumping a pound of grease into each side for weight training. Are you sure those on the axle are grease nipples and you are not confusing them with the small allen screws at each bearing housing? The bearings themselves will be double shielded cartridge bearings, so need no grease in maintenance. The axle shafts may be lightly greased to resist corrosion, so need no additional grease in maintenace anyway.
The grease nipple on the two wheel drive unit may be used to add a small amount of light oil in the hope it gets to the freewheel bearings, but the freewheels have some oil shields and of course 2 of the 4 bearings are internal and totally protected. In a similar question a few months ago Tuggo also said there is no point in pumping oil in here because most will escape anyway.
I'd recommend replacing the heavy Sachs freewheel based TWD with a Trykit cassette based unit for two reasons. Firstly, Sachs/Maillard sprockets are like hens teeth. Secondly, it is a heck of a lot lighter. Even George Longstaff himself noted that when he compared (about 6 years ago) his new cassette based system to the old one, the trike seemed to pick up more quickly with the new one.
The noise you heard is because you have added oil to one of the outer bearings, disturbing the rusty mess around the ball bearings. This will fade. The only way to grease these bearings, as with any freewheel, is a total strip which is beyond most people.