I have the same issues with maintaining humidity in my incubator, and often encounter the tough white membrane situation. I will tell you what i have done and what my experience is, but i would hate to steer you wrong as i am not a totally experienced "hatcher" (only 4 hatches under my belt - but one had 22 out of 22 live chicks! - a few of them helped). In fact i just had to help a chick three days ago out of a two egg hatch - and took pics if that would help. Anyway, after stressing and reading everything i could find on helping chicks, this is the approach i take when that touch membrane appears.
First - you need to give the chick 24 hours between pip and helping. I know it is a stressful time, and you are excited, but the little one is working hard inside that shell to prepare itself for birth, so let nature take its course. If nothing seems to be happening after that amount of time, i pick a bit of shell away from the pip, CAREFULLY, just chipping tiny pieces off. In my exp if the membrane is dried out and the chick is ready, then there are no fragile blood veins to contend with, sometimes there is even an air gap between the membrane and shell. At ANY sign of blood, or a wet vein in the membrane, immediately stop and wait for those veins to dry out! On the dried membrane eggs i seem to be able to chip shell off with no problem, and i go about a quarter of an inch (not opening the membrane, JUST removing the shell). You can easily see at that point if the membrane is indeed the problem. I then use a small BLUNT pointy object (i use a small Star awars toy gun - lol) to rip open minuscule bits of the membrane. At that point you will see the chick inside opening and closing its beak, and often it will chirp at you. After opening a quarter inch i know it is getting air, so i leave it a half hour and see what it can do on its own. If no progression then i chip off more shell and do the same with the membrane. Remember if there is ANY blood then stop - the membrane is NOT ready to be opened. i follow this method until the egg has been unzipped with my help almost half way around. Then I leave the chick to do the rest itself, which can often times be a couple hours. Do not rush the chick - even though you are excited. The baby needs time to dry out inside the shell so it does not pull its insides out when it detaches from the bottom of the shell. I have found the chick will pop off the top of the shell and rest a while before separating from the bottom of the shell in circumstances where it has been helped. I have been lucky, and every chick i have helped has survived with out problems, although i am sure there are plenty of posters that will have an entirely different perspective and disagree with me strongly.
If you would like to see pics of this process, and can post your email, i will send them to you. You can also skype me at intense1117 and i can answer questions. Good luck with your hatch! It is a exciting and stressful time. I have clocked countless hours staring into the bator, and i have also worked on the computer in bed, with a struggling new chick wrapped in a washcloth tucked inside my tank top to keep it warm, lol. My family thinks i am nuts. I also send out birth announcements to my friends when i hatch new babies. My current newbies are fluffy and spot - white leghorn and hooudan mix.
keep the faith!!!