Unusual? Yes. Out of keeping with current societal trends? Yup. But sick?
That guy in Austria is sick. The one who kept his daughter in a dark cell for half her life. They're now saying he probably raped the 18 year old too. She is both his daughter and his granddaughter. That is sick.
Physically, sexually or emotionally abusing your children is sick.
Having a larger family than most people would want is not inherently sick.