Perception

[Adam]

LDUB,
They've already drawn an arbitrary line in deciding he can't work the plate if his brother is pitching. I would say they need to take it a step further and say he can't work games for his brother.
As for how far they take this? Case by case. In general, I'd say that immediate family should be far enough. Father/son, brothers, etc. Uncle/Nephew? Hard to say without knowing the two involved, but I'd be inclined to let it pass.