Is it obligatory to obey a father who prevents his daughter from communicating with her brother, claiming he is corrupt and causes problems?

Obedience to the father is not obligatory in disobedience to Allah, and severing ties of kinship is forbidden. If it is possible to maintain ties with the brother without the father's knowledge to avoid his anger, that is preferable. Maintaining ties of kinship is obligatory unless it results in harm; if it results in harm, then there is no blame in severing them.