If you're assuming a fixed viewer, it's actually pretty easy to define position and time. There are just relativistic corrections to a bunch of the terms.
Only if you assume no acceleration on the objects. But he said charge, so they do accelerate.
You'd have to figure out the position and velocity of each one relative to the others to figure would what the effect of the charge will be. And don't forget to include the propagation delay of the charge field.
This is by far not a simple problem. Much much harder than the N-body problem.
If the top poster had only left out "Physicists are ridiculous." it would have been quite an insightful post, instead it was an inciteful one.