Honestly, I know a real-life couple who have dark brown hair and have blonde kids. It's the running joke of the family that dad isn't the father and mom slept with the milkman. But the kids have dad's eyes so we know it's his kids.
Genetics and DNA is such a mystery, to be honest. Granted this is a computer game so it could be more random than we would like. One of my best friends comes from an Italian family. Dark skin and dark hair. Dad and mom and BOTH sets of grandparents all have dark brown eyes. His brother and sister both have the same brown eyes, but somehow, beyond anyone's realm of understanding, he has crystal blue eyes, but still the same dark complexion and dark hair. There's no explanation sometimes.