When his wife arrived in Manchuria, O'Neill told her bluntly to learn Manchuria or she'd be useless and she'd have to go home again. She stayed, they ended up having children, of which three survived. One of his grandson's ended up writing a book about him.
It was not an easy mission field but by the time his time in Manchuria was over, he had a school, a hospital and a church. Converts were not easy to come by. Life was very difficult for missionaries living in China, conditions were tough, but they were made of tough stuff and stuck it out, expecting to die in the Land they were sent to. They made it their home.
O'Neill spent some time in the Chinese Labour Corp during WWI in France. His work was to help the Chinese Migrant workers. For this he received the Order of the Striped Tiger from the Chinese Government. His grandson needed to buy the medal back from auction. You can find that story here.