Is this rare or is this common in the NFL that family members are on staff?
I'm tempted to say that those who don't do it are actually the "stupid" ones.
Ryans (Rex Ryan daddy), Schotteheimers, Shanahans, Grudens, ... etc. Norv Turner's son is Cam Newton's QB coach. These are the family members we actually see, because of their positions/roles. How about those we don't even see because their jobs might be to reserve hotel rooms or provide food, take pictures, do marketing, ... etc.
In the meantime, those that have played the game and given sweat and blood to enrich the NFL ... can't even get a job with the NFL after they retire ...