Neddy do you want to work with me to understand what I'm saying because you seem to be under the impression that I'm proposing an alternative to SR that is trivial, inferior and has no real purpose?
You're right, that is pretty much the impression that I am under. Choosing a third party inertial reference frame where both the stay-home twin and the traveling twin have velocities of equal magnitude (but in opposite directions) is certainly something that SR allows, but it doesn't really shed any light on what SR says is going on in the other inertial frames of interest. Doing so specifically shifts the attention away from the very inertial frames about which the twin scenario was meant to be instructive.
For example, the stay-home twin would insist that their velocity relative to the ground they are sitting on is always zero, (the scenario assumes the stay-home twin never accelerates, so they would say that they are just sitting still, waiting for the traveling twin to return). That twin should not have to consider a different reference frame in which their own velocity is not zero. Indeed, if you want to know what SR says about the timing of events according to the stay-home twin's own inertial rest frame (where their own velocity is zero), then you really should consider that reference frame! But you want to disregard that, and instead consider a different reference frame where the stay-home twin's velocity is not zero. Very strange.
If so, let's discuss one point at a time. Have I mathematically misrepresented how SR uses length contraction and time dilation to explain how c=c from all perspectives since I have blindly come on the side of length contraction being real? The coordinates I came up with, are they any different from what the Lorentz transforms would give? Are the Md's incorrect in any way? If you're unsure of giving a blanket approval, I'll go into far more specific questions.
I was glad to see it when you started accepting that length contraction is a necessary part of SR. I was also glad to see it when you started accepting the constancy of c in all inertial frames as part of SR. But I am still not sure how many other aspects of SR you have yet to come to terms with.
It seems bizarre to me that you would spend so much time and effort to build a whole model which you thought was equivalent to SR, and yet not realize that something must be wrong as soon as it resulted in the non-constancy of c in all inertial frames. The constancy of c was known experimentally before SR came along. One of the reasons SR was developed was to tease out all of the ramifications of that. You should have known that it was one of the most important things to maintain, if you thought you were doing SR. And yet you decided it was okay to continue on without it. Likewise with length contraction, which although it had not been known experimentally, by the time SR was developed it was clear that length contraction was required in order to maintain the constancy of c in all inertial frames. And yet again you decided it was okay to continue on without it.
I am also leery of your terminology. You never seem to speak in terms of inertial reference frames, but rather you speak of "perspectives". Using the word perspectives sounds vaguely like you might be considering only what observers can see with their eyes. Of course the speed of light being finite will result in delay times as light signals travel from emitter to receiver, but SR is supposed to be what remains after those types of delays are factored out.
Even if you are finally doing the maths of SR properly, but just using a particular third party reference frame, (I honestly have not checked the maths or diagrams lately), and if you are obtaining the correct time and space coordinates in your chosen
third party inertial reference frame,, unfortunately those are still not going to be the correct time and space coordinates in any of the inertial reference frames which were of interest in the twin scenario to begin with.