Complex sentence: His grandfather, Arthur, was the first professional boxer to appear at the original National Sporting Club, and his father and uncle (Dick and Jack) were the Gutteridge Twins recognized as the premier cornermen and trainers in Britain throughout the 1920s and 1930s.
Split into simpler sentences: His grandfather, Arthur, was the first professional boxer to appear at the original National Sporting Club. His father and uncle (Dick and Jack, the'Gutteridge Twins') were recognised as the premier cornermen and trainers in Britain throughout the 1920s and 1930s.