Different FPS on different clips (premiere pro)
What you want to use to have a clip play back at a lower frame rate is the Posterize Time effect. It's pretty straightforward and self-explanatory. Just find the effect in the Effects panel under Video Effects → Time → Posterize Time and apply it to your clip. Then select the clip, open the Effect Controls panel and set the Frame Rate parameter of the effect to 8 (in your case). Then you're pretty much done. 

To apply that effect to multiple clips at once, you can use an adjustment layer. Create a new adjustment layer (File → New → Adjustment Layer) and put it above your clips in the time line. Then apply the Posterize Time effect to the adjustment layer. It will affect all clips in all video layers below the adjustment layer.