If the bus is moving and we are sitting in the bus then will we considered as motion or not and if so then why?
It all depends on the frame of reference of the observer.
If the observer is in the bus, their frame of reference is the bus. Relative to them, you’re motionless, whether the bus is moving or not.
If the observer is standing by the side of the road and the bus is moving past them, their frame of reference is the road, and you’re in motion relative to them.
If the observer is in another bus, their frame of reference is the other bus - and depending on whether it is moving at the same speed as your bus or not, you might be in motion or relatively stationary.