Complex sentence: They had two sons, James Preston and James Laidlaw Jnr, both of whom also became medical missionaries; the younger J.L. Maxwell served in the Tainan hospital from 1900 to 1923.
Split into simpler sentences: They had two sons, James Preston and James Laidlaw Jnr, both of whom later also became medical missionaries. The younger J.L. Maxwell served in the Tainan hospital from 1900 to 1923.