blockchain.info – Avoiding fees collecting BTC deposits from different addresses

We’re looking into making website for trading Bitcoin.

Users get individual bitcoin addresses to deposit BTC.

How do we avoid paying transaction fees for every of these deposit transactions that we’ll have to ‘repeat’ to send money to our ‘system’ wallet address?

We’ve played with bitcoind json-rpc. Could blockchain.com API help in aggregating this deposition payments without fees?

Thank you