You can’t have more than one pair of birds in the cage for breeding. The young female probably was trying to harm the eggs. Breeding birds are territorial, and if you have extra birds in the cage, the birds will end up fighting and raiding each other’s nests, destroying eggs or killing the chicks. You either need to take the nest out and not breed them, or remove the extra birds. As for the young finches, they should be kept separated by sex until they are at least 18 months old. Otherwise they will start to breed very soon, and they are much too young to be breeding. Finches can be sexually mature at 6 months old, but even though a bird may be sexually mature, it will still have some physical and emotional development to go through before it will be a good breeder. Young birds that are encouraged to breed too soon will often not take care of the eggs and are very likely to develop bad breeding habits that will ruin them for ever being a good breeder. And young hens are at a high risk of becoming egg bound and dying due to underdeveloped muscles. That young female is already exhibiting an interest in breeding by getting into the breeding hen’s nest and trying to break the eggs. It’s also very important that you find homes for any offspring. You should never let related birds breed, and parents will bred with offspring, or clutch mates will breed with each other unless you separate them.
Thank you for asking Lafeber,