In the bank transfer instructions for the opening of the account, under the heading "beneficiary" the name of the broker must be indicated.
"Will the money become their property and I will be able to operate on the markets by increasing the cost of the various operations (such as prepaid card) or will the money remain mine and will they take the various costs of the operations carried out?"
According to the information we have, the money does not become absolutely the property of the broker, even the transfer should go on a segregated account of it where you are able to dispose of that money through operations, withdrawals, deposits, etc. ...
The same thing would take place for any broker who deposits customers' money on segregated accounts such as TradeStation, AMP Futures, etc ...