taking the hobbits to isengard

I was able to do it, so it's not glitched overall. It may however be glitched for you. I didn't look at any other threads to see how others did it, but here's how I unlocked it.

I used the map stone to port to Isengard and moved outside it a few steps. Then I switched to Frodo and walked inside. I walked back out, switched to Sam and walked inside. I repeated that with Merry, Pippin, Bilbo and Rosie and when the last hobbit walked in I unlocked the achievement. I used the basic version of each hobbit that had multiple versions available, but I am not sure how important that part is. I'm also not sure that I needed to walk outside between each hobbit, but that is what I tried first based on the theory that each one needed to cross the threshold on their own.