As far as I know when a person travels with some velocity relative to other person time runs slower to him relative to the other person (Because the velocity of light is constant in all frame of reference). This I have understood from twin paradox. But this becomes complex to understand when it is more than twins.
For example, here is a thought experiment,
Imagine there is a huge treadmill covering the entire circumference of the earth and there is a vehicle situated on that treadmill belt. Now there are three twins( twin A; twin B; twin C). So here twin C gets into the vehicle, twin B hold on to the treadmill belt(so that he moves along with the belt) and twin A is standing in the ground(stationary).
Now the vehicle starts to move in 99% of $c$ (speed of light) and the treadmill starts to run in the opposite direction with the same speed of the vehicle so that the vehicle appears to be stationary to twin A.
So here blindly applying the theory which was applied in twin paradox time running for twin B should be slower than the time running for twin A. And time running for twin C should be slower than that of twin B. But now if we suddenly neglected that treadmill from our experiment(Let's say it becomes invisible) now this makes no sense as the vehicle looks stationary to twin A and so the time should run in equal speed for them. So what will actually happen in this thought experiment?