There is no such thing as a perfectly rigid body. These might have a place in your fantasy physics, but if you want to do real physics, you will have to leave them behind.
Pulling apart requires a difference of force in a direction. If you bother to work through any example in detail, then you will see a difference in force. In the case of the Bell’s Spaceship Scenario, there is a much greater force in one direction.
You are still thinking in terms of an idea of time that simply doesn’t match up with our universe. That’s fine, but if you want to criticize special relativity, please learn special relativity.
I have no idea what you mean here. Given your problems understanding what the relativity of simultaneity is, I suspect that you think that if something is fixed as simultaneous once it is simultaneous in all frames of reference. This is not the case.
Perhaps you didn’t notice those engines pushing and pulling the train or the spaceships?
All objects are in all (well-formed) reference frames. One cannot infer anything from a claim that an object is in a reference frame other than that the reference frame is sufficient to describe the object at some spacetime event.
You fail to see that you are not describing physical scenarios accurately. If you did, you would always find that there was the same result when the same treatment was applied. However, you describe sloppy scenarios where you leave out important factors or include contradictory ones (like claiming that some events are simultaneous in all reference frames).
The string has a reason to break: the laws of physics governing electromagnetism. You deny these laws, at least to the extent that you refuse to look at them or learn them.