New Bitcoins changing possession and how can we own fractions?

Hello!

I have been exploring and studying the underlying logic and features of Bitcoin and I have some further questions I would really like to get answers for.

So, news Bitcoin come up from block rewards after the hash for a new block is found, right? (Correct me if I am wrong.) How does the miner gets final ownership of those Bitcoins? When new Bitcoins come into existing are they already tied to a new pair of public and private keys?

And what happens to the private key that holds bitcoins once once that key no longer has bitcoins associated to it?

And with all these keys can we have multiple public keys pointing to the same block giving ownership of a certain amount of Bitcoins to certain individuals?

Thank you for your help!