Fels had a keen interest in history and classics, but rather than going to university he became manager of the family's woollen mill near Paderborn.

Willi and Sara had three daughters Helene, Emily and Kate; and one son Harold who was killed in World War I.

Fels eventually became managing director of this firm and the connected Drapery and General Importing Company.

[1] Fels was an avid collector, and his journeys through the young colony on business afforded him the opportunity to collect Māori and Polynesian art and artefacts.

[10] Fels' family were prominent in the arts and culture of southern New Zealand for many years, his cousins, the De Beers (including Esmond Samuel de Beer), and grandson Charles Brasch also making a permanent mark on the country's cultural life.