1. Here, I am confused in this blue highlighted paragraph, it's totally gone over my head.
2. and if two parties sent coins simultaneously at one address what will happen, I think they both transactions will processed in same block, and no problem is faced like coins not received or only one transaction is approved ,
is it right.?
1. It is a complicated way of saying that reusing an address reduces your privacy.
First, the presumption is that someone sending coins to your address knows who you are (or at least something about you). If you never reuse an address, then a sender knows only about the coins that
they sent to you. They don't know what other people have sent you because they only know about the address that you gave them. When you reuse an address, then everybody given that address knows what everyone else has sent you.
2. There is nothing preventing or prohibiting any number of people from simultaneously sending coins to the same address.
means we can generate, multiple addresses with same private key, and they all will show equal amounts in all created wallets...
It doesn't mean that. Also, a private key is generally associated with a only single address. While, a private key can be associated with multiple addresses because there are different address formats and transaction types, it typically does not happen.
You are probably thinking of a HD wallet that generates multiple private keys (and their addresses) from a
seed (via a
master private key).