Complex sentence: His two daughters lived with Mary Anne Payne Clew Blumenthal in Brookville, New York, with whom he was having an affair, and with whom he had phone contact from Portugal until the FBI cut them off.
Split into simpler sentences: His two daughters lived with Mary Anne Payne Clew Blumenthal, with whom he was having an affair, in Brookville, New York. He was in phone contact with Mary Anne from Portugal, where he was based, until the FBI cut them off.