How can one strike a balance between pleasing the erring father who prevents contact with the brother, and the brother whom the questioner has no one else but him, given the father's threat to deport the questioner from the country?

You must strive to advise your father and brother concerning prayer, offering them books and tapes related to it, and reminding them of Allah and the Last Day. You should also advise your brother to be dutiful to his father, and advise your father to maintain ties with his son, and try to reconcile between them. If they do not respond, others can mediate. If that does not succeed, then you must be dutiful to your father and obey him in matters that do not involve disobedience, and continue to advise him and pray for him. Do not sever ties with your brother, but it is permissible to abandon him as a form of deterrence, not abandonment, if that is more beneficial for him to return to what is right.