The membrane is whats directly under the shell, right? May be a silly question, but its turning a yellowish color not sure if thats normal. I'm almost positive one will or should be hatched by morning. Not sure about the others yet.
Yes the membrane is the thin flexible layer between the shell and the chick. There are actually 2, an inner and an outer. Both are encasing the chick until it breaks into the air cell, so an internal pip, it’s beak is thru the inner but not thru the outer. Once it breaks the shell, the outer membrane is broken too.
So if the pip hole is open enough to see in, the outer membrane is closest to the shell, so you may see the edges of it.
Yellow could be the start of brown. It normally should be white to wet-gray looking. Yellow isn’t too alarming unless it gets darker. The yellow could also be from a little bit of fluid from inside the egg.