Question

draw position time graphs for two objects having zero relative velocity

Answer 1

zero relative velocity means the two objects are either stationary (both), or they are separated by the same displacement all the time.  That also means that they both have the same speed, velocity and acceleration.  They move in the same direction.

So the acceleration - time graph will be exactly same for both.  The velocity - time graph will be identical too.

The displacement (or position) - time graph will show two parallel curves, separated by a vertical difference (b-a) as in :

          s1 = a + u t + 1/2 a t^2
          s2 = b + u t + 1/2 a t^2

Answer 2

If two bus are moving with same velocity and passenger frame within bus fell is at rest vA= vB

So relative velocity become zero

Option 2 is correct