The main argument used to solve the twin paradox is based on the accelerations and decelerations of the observer considered to be in motion. In the twin paradox of the version described here, accelerations and decelerations are bypassed, thus the main argument is disarmed.
We consider three twin brothers, Mov (moving), Sta (stationary) and Rem (remote). Initially, Mov stands 100 meters behind the Sta and begins to accelerate his movement towards the Sta. The moment Mov exceeds the Sta, its speed stabilizes, their clocks synchronize while at the same time the experiment begins. The final speed of the Mov is not great, while the age difference from the Sta due to the acceleration is negligible. Therefore, from the start of the experiment the acceleration has been canceled and the relation of Mov to Sta is symmetric.
Mov continues his journey for millions of years, moving towards observer Rem. Rem is immobile in relation to Sta, so he was able to synchronize his watch with Sta during Mov's journey. Towards the end of the journey, Mov approaches Rem close enough to discern his features. Once that happens, Mov stops.
At this point, it is obvious that the ages of Sta and Rem are the same. In addition, there was no acceleration or deceleration of Mov throughout the experiment, which means that Mov's symmetry relationship with Sta is not broken. Consequently, the ages of Mov and Sta must have been the same when Mov observed Rem's features on the move. Thus, as the three observers of the experiment were twin brothers, Mov must have found that Rem was exactly the same as himself shortly before he stopped moving. So the age difference is zero.
From the above result it also follows that if a fourth observer had stood at the starting point of Mov's journey and they were synchronizing their clocks before Mov started moving, then the initial acceleration would not make any age difference throughout his journey Mov.
So, when the spaceship of the classic version of the twin paradox returns to Earth, a disgruntled old man will come out of it, as he had believed that his journey would last a few years. No one had warned him that he was likely to spend the rest of his life in solitary confinement. I believe that this result can only be explained in the context of quantum physics.
An unjustified reply has been deleted, but some clarification is needed:
The main argument is that in a state of absolute symmetry no time dilation can be justified. If you have a counter-argument, then I would ask you to at least outline its main points. This would help a lot.
Answers to comments
Rob: Then the twins will have a common age after their return to Earth.
gandalf61: This problem is technical, it does not change the substance of the arguments. There is no law that forbids the existence of two identical people at any distance at the same time, and that is enough for us.
SamuraiMelon: See it like this: You can think of Mov as immobile and his siblings moving in relation to him. The results of the experiment would be exactly the same according to Relativity.
Charles Francis: Clocks can be synchronized by exchanging light signals. Einstein describes how this is done in his main article. You may notice, however, that I do not use the indications of the clocks in order to draw the final conclusions of the experiment.