You don't need to use 8 direction or sprites, you can use the 'scroll to' action and some maths to determine your speed and direction.
Create 4 static variables: TouchStartX, TouchStartY, TouchAngle, TouchDistance.
1. 'On any touch start' you want to set the TouchStartX&Y variables to touch.X&Y
2. 'Is in touch' you want to set the angle and distance variables to: angle(TouchStartX,TouchStartY,Touch.X,Touch.Y)-180 **-180 is to reverse the direction.
distance(TouchStartX,TouchStartY,Touch.X,Touch.Y)
As a sub event of 'is in touch' you can use the
3. 'scroll to' action and set the values to lerp from the current scroll coordinates to the angle and distance of the touch action.
lerp(scrollx,scrollx+cos(TouchAngle)*TouchDistance,1-dt*0.5)
lerp(scrolly,scrolly+sin(TouchAngle)*TouchDistance,1-dt*0.5)
4. 'On any touch end' reset all variables to 0.
For your UI elements, create a new layer on top and set it's parallax settings to o. This layer won't be affected by any scrolling and your buttons and text will remain in place relative to the viewport.