Hatching under a Broody

One of my Jersey Giant went broody. So, we stuck about 8 Guinea eggs under her and 4 Easter Eggers laid under her at some point, not sure when those will hatch. The Guineas started hatching on Friday, Day 25. I got 1 at about 830. I went to check again at midnight and it was dead, crushed under mama and the eggs. Mama kept pushing it in with the eggs instead of under her wing. I got another at 7am, I took that one out and put it under a light. It started eating and drinking doing great. This morning I got two more. I thought it was 24-72 hrs most of them would hatch. I'm on day 28 now. How much longer should I wait for the others to hatch before I give up on those eggs?