Two trains moving in the same direction and at the same speed will be ___.
at rest with respect to each other
in motion with respect to an observer standing outside the train.
Rest and motion are relative, a body can be in motion with respect to an object and the same body can be at rest with respect to another object.
When 2 trains are moving in the same direction with the same speed, the passengers in both the trains are at rest with respect to each other.
While to a person standing outside the train both of them will be in motion.