Yeah, you don't want them to breed if the babies are dying within the first few days, this most likely means that mom and dad are not feeding them appropriately, or at all, or they are harming them or killing them. The fact that she ate her first entire clutch since you got them is a bad sign too. You have no experience in hand-raising/feeding baby birds, let alone from 1 day old, which is extremely difficult and not for anyone who hasn't been trained by a mentor and who doesn't have any experience. It's hard enough from 2 or 3 weeks old, the time that most breeders pull the babies from the nest boxes. But if you have to remove day-old babies and hand-raise/feed them without any experience, they are most likely going to die anyway, one way or another. It's extremely easy to aspirate the hand-feeding formula into the lungs of a day or so old baby, and when this happens they die instantly, literally instantly. You also have to feed the babies once every 2 hours for the first two weeks, AND THIS INCLUDES EVERY 2 HOURS THROUGHOUT EVERY NIGHT, OR THEY'LL DIE. Then at 2 weeks it's once every 3-4 hours including throughout the night. ONLY AT 4 WEEKS CAN YOU GO TO FEEDING THEM ONCE EVERY 4-5 HOURS, AND CAN THEY GO FOR 6 HOURS OVERNIGHT. It's exhausting and difficult, and heartbreaking.
Usually when a successful breeding pair starts eating their eggs and having newly hatched babies die quickly, it's a sign that they don't want to breed anymore, or something is wrong and they shouldn't be breeding anymore. or MORE THAN LIKELY THE BREEDING PAIR IS TOO OLD TO BREED, OR HAS HAD A PAST HISTORY JUST LIKE THIS AND THEY WERE NEVER A GOOD, RELIABLE BREEDING PAIR, AND YOU WERE LIED TO, THAT'S PRETTY COMMON TOO.
And if you're not using a nest box and don't know the basics, then you shouldn't be breeding birds at all, period.
Have you seen them mating recently? Have you been candling the eggs to see if they are fertile? First of all, you can replace the eggs she lays with plastic eggs immediately, and put the newly laid eggs in the freezer overnight to ensure they are dead, then pitch them. Keeping plastic eggs where she laid the real ones should stop her from laying anymore. You need to shorten their days and lengthen their nights by adjusting their light, and this will help to stop them from mating and stop her from laying more eggs. So putting them in a room that you can control the sunlight/light in is very important.