QQ:
so why assume it transits vacuumous space and is not some sort of entangled mass inertia phenonema?
Because I've never heard of an entangled mass inertia phenomena. What's that?
The reference frame consists of two observers back to back with high explosives packed in between them.
I explained what a reference frame is above. A reference frame is not an observer or an object. But I'll accept that you're using a reference frame that has the observers at rest initially.
both observers in this Initial RF have identical ticking clocks and can consider themselves at rest relative to each other. So relative velocity = zero between observers.
Yes.
The following image shows the two observers ungoing identical accelleration. at no point is their velocity different. The only difference is their vector.
Wrong. Velocity is a vector, as I explained above and you ignored.
Two objects moving in opposite directions have different velocities, even if their speeds are the same.
During this step the observers could be said to still maintain a relative velocity of zero at any point in their simultaneous acceleration.
No. They may have the same speed, but that's not the same thing. Also, their accelerations are different, because acceleration is also a vector and they are each accelerating in different directions.
As their relative velocity at any point during acceleration is zero...
It is never zero except right at the start, before they start moving.
and at no stage do the clocks tick out of synch as both observers are experiencing exactly the same acceleration conditions.
Acceleration has nothing to do with it.
Also, the clocks tick out of sync in the frame of either of the clocks. Only in the initial rest frame do they continue to tick in sync, and only then because time dilation depends on the speed and not the velocity.
Important Note: The Initial RF no longer exists yet is still relevant.
A RF cannot cease to exist. Did you read my post above at all? It is quite insulting to have to repeat myself because you do not do me the courtesy of reading my posts.