In post #3 the 3rd and 4th photographs both show significant damage to the threads on the fixed axle.
I doubt that you will be able to tighten the nuts sufficiently, no matter how many locking washers, torque arms and split washers you put on, in order to stop the torque twisting the wheel out of the dropouts.
You might get lucky with a thread restorer nut, or a thread file. Don't be tempted to use titanium nuts, stay with steel.
Clean up the rust, repeat, clean up the rust and smear a very very thin layer of waterproof grease with your finger on the exposed surfaces.
Good luck.