I just had the same thing happen to me earlier this week -my first batch of turkeys ever. I set 13 eggs(also 6 chicken eggs) and on day 27(Tues) four started to pip and then stopped. I ended up peeling open the four and then opened all the other eggs. I looked like several of the turkeys had died within a few hours before I decided to aid them. They were perfectly formed and still soft. 7 turkeys and 2 chicks survived me cracking them open.
I also use the 1588 hovabator. I was reading the instructions that came with the incubator and it stated the humidity at lockdown should be at 55%-65%, but after reading on here some people are suggesting 70%-80%. I'm going to try that next time. I had a batch of chicken eggs before this one that I had to help all the chicks out of. I'm thinking the humidity might have something to do with it, as the membrane looked dry when I hatched them out.
I know people discourage manual hatching, but I would definitely help the others out, at least they will have a chance. In the past 2 months I've had to manually hatch out 25 eggs(out of these, only 9 had pipped). I now have 14 chicks and turkeys that otherwise would have died if I had left them on their own.
Good luck!