After incubating the eggs for 5 days there were still no signs of life so I decided to crack one open. It was just a yolk, no signs of any chick development. I decided to crack the rest and they were all the same - just a clear egg, nothing but a yolk inside. This means the eggs were never fertilized or just never developed, and the process of laying them likely worsened Peach's condition. While I am sad about the eggs I am also relieved, I promised Peach I would try my hardest to save her babies but in reality there were no babies to save. I can mourn her now fully and know that the eggs would never have hatched even if I were to have began incubating them earlier.
Now about Peach. As you know, she had been pooping blood the night before I found her gone and it was the only symptom she ever exhibited. In the initial necropsy the vet saw that Peach's crop had food in it, her lungs and heart looked normal but her digestive tract was empty and her kidneys and liver were very pale in color. They get specific results back today from ISU so I will update with another post then and I will be glad to know for sure what it was. Overall the cost of it was $45 for initial necropsy and to send her organ samples for testing was $170.
Boo is now my only bird and he is still eating, drinking and pooping normally so I know it was not likely a contagion but something she was possibly born with, disease of some sort. I will update when I have a solid answer on that and will make a new thread for her in remembrance but I wanted to thank everyone for their kind thoughts and prayers during this time. I am still recovering from the loss of Peach but Boo seems to be okay. I have to remember that birds are much more simple minded than humans are, I don't think he wakes with dread in the morning knowing she isn't there or feels sad. Just lonely. I moved him to another cage with no more nest box as he would not let me take it out of his old cage (despite no eggs or mate inside) so I had to towel him and move him that way. But within minutes of it being out of sight he was just fine, no longer aggressive to me and just wanted to come out and sit on my shoulder. Out of sight, out of mind maybe.
To those who read this thread hoping to see some cute cockatiel babies, I am sorry this thread does not have a happy ending, but I hope it serves as a reminder that breeding birds can and will end in tragedy sometimes. But I still have hope. Once I know of Peach's cause of death I can move on and move forward. Boo will also move on, he likely has already. So in the summer/fall I will likely get Boo a companion, but for now we are a one-bird family and that Is okay.