As I'm not an expert but have had many parakeets. If the hen or female broke the shell that is fertile she may be helping the chick to break free. If she did this to an egg that is not fertile, she may have sensed this & wanted to eat the shell & contents. Both are very nutritious providing the hen with much needed calcium. In the wild they may do this to keep predators from going after an egg that's not fertile or even an embryo born dead.
no no no
sometimes
vff
its not a good idea because the new one will probably get too cose to the egg
to keep the egg warm, and to protect it.
YES!
check
no. it is just like touching an egg
After the parakeet molts and starts looking older it will soon enough lay an egg.
18 days
Yes. But it will not be fertile.
If it is a single parakeet--leave the egg in the cage till it gets cracked.this is suppose to discourage from laying more.