I'm probably the least qualified person on this forum to answer, but it sounds like my batch is a few days ahead of yours, so... Once they're actually "hatched", you'll know, cos they're out of their egg sacks and they'll be lying on the bottom or wriggling around in the water.
As to whether you should help them out, I only know that the Axolotl site says:
"Once most of the larvae have hatched, it is a good idea to tear the jelly coat of those eggs that haven't hatched yet in order to free the larva inside. This can be done with a sharp forceps or narrow scissors that is inserted into the egg and then the prongs/blades are pushed apart."
I have the same question as you really, as only about 12 of mine have hatched so far (that I can find!), and I'm wondering what to do with the rest - leave them, or help them out? Some of my babies already didn't make it :sad: :sad:, so let's wait and see what everyone else has to say...