All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
It is permissible for you to send money to your sister in order to distribute it as you wish as long as your brother does not abide by what you tell him regarding distributing the money you send to him. However, you should do this wisely as a way of keeping affection between you and your brother and being kind and dutiful to your father. This can be achieved by sending to him what you want to give to him and to your parents, and you may send to your sister what you want to give in charity and to your relatives; in this way you will combine two good things (pleasing your father and brother and distributing your money as you wish) without your brother knowing about it. Thus, a wise person may achieve his objective with softness, gentleness and wisdom.
Finally, it should be noted that it is not permissible for your brother or any other relative not to abide by what you tell them to do regarding distributing the money you send to them as they are your agents (whom you authorized to do something) and an authorized person is obligated to do what the authorizer tells him to do.
Allaah Knows best.