hi and welcome 
You could make a loop, so:
1- Input window asks you how many chapters? so you type 8, then the loop will run 8 times.
2-The loop can be something as simple as finding the top-most icon in Scrivener, copy text, then switching to the other app
3-Next, it returns to Scrivener, moves mouse N amount of pixels down to find the next chapter, then starts the loop again.
As for the Edit button in Vellum, how did you try to do the click? Using KM's Found image?