Re: How to send balance from multiple address to a single address?
Can I ask why do you want or believe you need to consolidate all the BTC into one address? 
When I want to sell the btc, I need to transfer all the balance from clients btc addressess to my exchange btc address.
so, that's the reason.
If your wallet contains all the keys belonging to those addresses, then you will be able to spend the all the coins regardless of what address the coins are associated with. Your wallet software should handle that just fine. By consolidating all the coins together you're creating unnecessary transactions and wasting money on fees.
cant agree more