I read that you can tell if an egg was fertilized it would have a bullseye... do these look fertilized to you? I’m not sure about the third one.
And I also found a strange thing inside my normal looking egg?
Yes those all look fertile. I can see the little rings around the central spot.
Not sure what your weird thing is but it looks like a membrane that didn't make it to the egg stage maybe, that got caught up with another egg before the shelling process and ended up inside that egg. That's the best I can come up with but maybe someone else can shed some light on your mystery thing.