If im correct some females will kill the babys if not in a safe place for her to raise them or if she knows their bad.

My cockatiels laid 6 eggs. I don't know if it was last week or last month! I've had them for 5days now. I went to check eggs and one had a hole in it! I picked it up knowing the baby was dead, and I looked inside and seen a yellow ball. I picked apart the shell and it looks like a regular egg from a chicken... and the eggs are cold. My cockatiel will NOT lay on them. Male or female. I can't see anything in eggs when I candle them! Just a dark spot on one end. No veins. Nothing. I felt something moving in one egg.. but see nothing. Not even a dark spot. What's going on? 3 have a tiny round crack like maybe a beak?? I don't know.