So I will echo the train the wife and kids but I will also give you some arguments that will tend to work to start them on the path to being trained.
Arguments in order:
#1 - Honey, I would feel much better if you knew how to make the pistol and shotgun safe - just in case you ever have to. Then teach loading and unloading only.
#2 Honey, you know how to make it safe, I think the kids should be able to do the same.
#3 Honey, now that you know the basics of how to make the firearm safe, I’d like you to come with me to the range and practice loading and unloading for real.
#4 Honey, how about we make sure that you can actually shoot the pistol / shotgun properly. I want to know that if I am hurt or not there, that you can use these to protect the kids from a murder or a rapist.
#5 Wow honey, not bad, you seem to have some natural ability with these - can you hit a smaller target?
#6 You know honey, you are good enough that maybe we should send you to a formal instruction or class.
#7 From a safety perspective, the kids really need to know this as well.
That is a primary argument. "Honey, what happens if I forget to lock it up on the way out of the house, and kids have friends coming over. You need to know how to safely secure the firearm."
Stop calling it a WEAPON! A Bic pen or a 2x4 can be a weapon. Call it a gun, call it a firearm, it's an inert piece of steel, but it's not a WEAPON until it is pointed at someone.