CK - I'm sure there is someone that can give you much better advice than me. I think I just had some really good beginners luck with mine. I had no clue what I was doing...But, if you read the sticky post under Incubating & Hatching, I think that will give you a good starting point.
I couldn't even find any blunt tweezers. All I had was a bobby pin. I used that and broke off small pieces of the shell at a time. Then I also used a damp paper towel to soak the membranes as I went. And, yes, I started at the pip. Then went around like they do when they zip.
With the first one, I did a little at a time, then put back in the hatcher, then did some more until it could work towards getting out. With the second one, I didn't have time. It was in more of a dire need.
But, I would wait until you have no more pips in the hatcher. If you open it too much, you risk damaging the other, possibly more healthy, chicks. I waited until the last pipped egg hatched, then worked on the struggling ones. I still have 5 in the hatcher that never pipped.
Good luck. It's not as hard as you think...just remember to breathe. I think I held my breath the whole time. LOL!
Keep us posted.