I am also the family photographer that brings gear to all the functions and takes snapshots. I never charge for anything like this, except maybe print costs if they want a bunch of stuff.
However, I have found that there is a dividing line
When family members just expect you to take pictures and provide them with all the files or prints, and use you to avoid paying a pro.... that's the dividing line. Usually that line is even more clear if you know it is a family member that has absolutely no intention of paying for anything or even making you an offer as a considerate gesture. I am happy to help out where I can, but don't appreciate being used. If I am expected to do a pros work and bring a studio light or two to do formal portraits and everything else, I at least charge a flat fee for my time, then cost + for prints and processing.
You have to think about a few things... What happens when you take this gear that you are expected to bring and something gets broken? Do you expect them to take care of the damages? Do you have hard feelings because the damage would not have occurred had you not shot the event? Yes, there is insurance for those things, but not everyone carries insurance on their gear, and usually it is not worth making a claim unless something really expensive gets stolen or broken.
So, yes, I have done weddings for free in my family. Usually it is as a second shooter and with permission from the main photographer. I typically treat my services as a gift and let them do the printing. If I am the only shooter, I usually come to an agreeable rate for my time.