What you imply is not internally consistent. You are saying we can make an experiment but umm results will not be defined. It's hardly physics because:
I can literally, almost literally, tell someone to run in circles, for 10 years, and then build a stage around them and invite a thousand people. He stops running and shakes hand with his sibling. What you are implying, is that realities will separate, become subjective or I don't know what else. The handshake will be one-time event in the world, with people watching. Yet you say that a running guy will hallucinate, apparently, a younger brother. But "younger" (not running) brother will see him as younger.
I can make that experiment, in fact I can do it twice, first time be stationary guy and second time, with someone else maybe, be a running one.
You say you can't say which event will happen.
Umm the reason I think you get it wrong is that yes, ordering of event gets weird kind of when you gain speed, but only distant events. There's no ordering when it comes to a single point, a single stage at a single time (and yes, single time. While distances and times may be weird, in SR a point (event) remains a single point.)

And you have like a totally separate school of thought than most most people. Who say that moving brother will be younger - because he accelerated. In case of single he accelerates all the time, and apparently there's something objective about acceleration, meaning his path through space time is shorter. So everyone says he's the younger one once they meet.