Letting somebody off on a ticket isn't a "courtesy", it's kinda more like corruption. A courtesy is maybe waiving a late fee or giving a colleague first dibs on something. If the infraction would usually earn just a warning, it isn't a courtesy, it's everyday policy. If the infraction would usually earn a ticket, it's still not a "courtesy", it's letting someone get away with breaking the law.

In one of your hypothetical situations, I would tend to err on the side of caution, lest John Q. Public get the wrong idea. If I were the ticketer, I would say "Your mother is a cop, you should KNOW better! No way am I letting you off the hook."

If I were the ticketee, I would probably INSIST on the ticket, not wanting the possibility of someone accusing my loved one of favoritism or corruption.

Anybody who's truly angry because he/she got a ticket that he/she knew was deserved doesn't belong in law enforcement.
That's my story and I'm stickin' to it.