Complex sentence: Fred Micklethwaite continued the family business until 1941, passing it on to his son, John Harold Micklethwaite, the fourth generation of Micklethwaite in the photography business, who went on to become a commercial photographer in Toronto until his own death in 1983.
Split into simpler sentences: Fred Micklethwaite continued the family business until 1941, passing it on to his son, John Harold Micklethwaite, the fourth generation of Micklethwaite in the photography business. John was a commercial photographer in Toronto until his own death in 1983.