Their eggs do have strong membrane. I had one that popped but couldn't get thru it. I waited about a day, it was still chirping inside so I removes a small bit if shell and put a Lil hole in membrane then back under hen, few hrs later chick was out.
Yeah, my youngest got broody after only laying for a couple months, she was determined. So I let her sit on 5 eggs, of that 3 hatched, I think one was lost early on, but the other was like full grown in shell I don't know why it didn't even pip.
I was leaning towards 2 f, 1 m. But I don't know. Maybe the ones lighter color is just Genetic. They are 6 weeks and couple days old. Was thinking they should be showing some black by now if any are cocks.