If a group/family of humans is larger than 200, it will be ok. No genetic problems. That's pretty much only with brothers and sisters, cousins is not a good idea, but not necessarily harmful.
The human genetic code is quit complex, and problems arise, when there are too many similarities. Like brother and sister. It's sounds disgusting, but father-daughter, or mother-son is already considered safe, but of course immoral, due culture.
The best is parents with great differences. So go interracial.

Btw, blonde people won't be here in around 600 years, and gingers are to be extinct as well .