Complex sentence: The original Braniff brothers remained a part of the company even as the ownership was repeatedly transferred, until the airline was purchased by the Aviation Corporation (AVCO) holding company, whose other holdings included the predecessors of American Airlines.
Split into simpler sentences: The original Braniff brothers remained a part of the company even as the ownership was repeatedly transferred. Eventually the airline was purchased by the Aviation Corporation (AVCO) holding company, whose other holdings included the predecessors of American Airlines.