Based on the information I have read in the forum that blockchain wallet is a non-custodial, the who owns the private key owns the blockchain wallet and no one had access on it except the owner of the private keys or the seed phrase of the wallet.
No one has access to it except you. At least if you believe what blockchain.com is telling you. And if you are sure what code you are running.
If you aren't sure what code exactly is being run inside your browser, you shouldn't assume that.
Additionally, the encrypted wallet file is stored on their server. So you better choose a strong password. Or (which would be way better), you stop using web wallets and start using proper wallets (mobile-, desktop- or hardware wallets).
Bitcoin wallet can generate public keys from xpub which should not be disclose to anyone.
You shouldn't disclose the xpub because of privacy reasons and security implications in some specific cases.
But you definitely can without automatically having security issues.
The generated public keys had also corresponding private key (xpriv) and this could be use when one like to import bitcoin public key to other platform or bitcoin wallet.
The xpriv is the master private key. It is used to derive private keys.
You do not want to share private keys at all. That's the reason they are called private. They allow you to spend the coins associated to your public keys (and therefore to your
addresses).
To import a watch-only wallet (without the ability to spend coins), you need to import public keys (for specific addresses) or the xpub (master public key) for all addresses of your wallet.
Now, what will happen to the imported bitcoin public address with its corresponding private key to other bitcoin wallet to other wallet if the imported public wallet has a balance? Could I spend the balance when it was only being imported to the new bitcoin wallet?
Coins are "stored" on the blockchain, not your wallet.
They are associated to public keys. And the corresponding private key can access/send them.
So, anyone who has access to the private key, has access to the funds.