How do I know how much each address own in a wallet? My wallet has 3 address. One main address is shared with my other computer. The other addresses are not.

Does money belong to a specific address or to a whole wallet? What happen if I send money to one of my own addresses?

What happen if I delete some of the addresses?
Technically, bitcoins aren't sent to a wallet.  

The Bitcoin blockchain works as a ledger.  A "wallet" simply holds the keys that allow you to spend funds.

If you are simply asking how to monitor balances for certain addresses, there are third party services such as BTCBalance.net which make this possible.