I am not really sure if this is ATM or not. If not, please close the thread.
Anyway,there are various interpretations of the twin's paradox and various so called explanations for the twin's paradox.
I propose the following interpretation.
O and O' are in the same inertial frame.
O applies a constant acceleration and so does O' in opposite linear directions but for different time periods such that their relative motion is v.
O apples the acceleration for the longer period.
They agree to proceed with this relative v for a long period of agreed upon time.
Then O applies a constant acceleration in the opposite direction of the prior acceleration for the shorter time period.
O' applies a constant acceleration in the opposite direction of the prior acceleration for the longer time period such that they are forced back to the original inertial frame but at a much greater distance.
They can then apply Einstein's clock synchronization procedure since they are now in the same inertial frame.
What will the clocks reveal?
Of course, SR claims they will both be dilated by the same value.