You can't discriminate based on membership of protected classes, and the doctrine of "disparate impact" means you can't have an imbalanced impact against a protected class (even if unintentional!), unless there's a reasonable business case.

Excluding blondes has a disparate impact against race.

Excluding people with a brother named Mike can be argued to have a disparate impact based on ethnicity or national origin. Excluding people with a brother named Mike but with no restrictions on the names of their sisters might be discriminating based on sex. The condition is also more likely to exclude people with larger number of siblings, which could be argued to have a disparate impact based on religion.

Good point, thanks.