Complex sentence: When Charles died, the business was carried on successfully by his sons, Charles, jr. and Frederick P. Stieff; the technical management of the factories being in the hands of Jacob's son Charles, who he had trained to be his replacement.
Split into simpler sentences: When Charles died, the business was continued successfully by his sons, Charles Jr. and Frederick P. Stieff. The technical management of the factories transferred to the hands of Jacob's son Charles, who he had trained to be his replacement.