It's a family: man+woman+ 3 sons. They might be teachable to shoot, but I would bet that they wouldn't pull the trigger even if their lives depended on it. Maybe I can teach them to plant or chop wood. Urgh.
Is this "showing up at your place" scenario a conversation you have even had with them - or is this something that is just a scenario that you and your wife are worrying about (because you know them and think it will happen)??
One place to start with this might ( if you have not discussed it with them already) - is to try to somehow gently bring it up in a conversation. Something as simple as mentioning a story you read about terror attacks - and how most people are unprepared to help themselves might do it. Then see what their reaction is. If you are worrying that this is something that might happen - and that they have not even thought about it yet, but they will inevitably end up at your place if the SHTF - then you owe it to everybody involved to somehow start the conversation.
You should also be aware that even opening the whole topic might be a massive can of worms. I have heard numerous stories of this topic starting some mighty fights.
One tale I remember was a person who (if I remember correctly) posted his experience on TheHighRoad. He lived in the NorthWest (Washington) about 20 miles outside a major city. And he described himself as "survivalist" in that he was prepared with firearms, food storage, fuel, generator - the whole works. His family also was friends with a bunch of other families in the neighborhood -which had expanded with upscale housing and was largely occupied with refugees from CA. Well one night at a party somehow the topic of conversation came around to what would happen in the face of a disaster - well a couple of the wives of said CA couples made comments about how they would all be coming to WA guys' house. As he described it - he made comments about how only had enough to help out his own family - and if they were worried about a problem like this they should prepare on their own - the wives went off on a tirade about him being a hoarder, they would call the authorities, etc. etc. This of course caused an even further fight - and the gathering broke up. The comment that this guy said he made that probably sealed the deal was telling them that if they tried coming into his house during a time of disaster bad enough they are running over to his house - that he would shoot them.
He did also end the story by saying that a week or so later he was talking with one of the husbands who told him that he had been thinking about what was said - and he was looking for advice on what kind of generator to get - and he wanted to learn how to shoot and wanted some firearms advice.
So my take on that whole story was that in the end the blowup was probably a good thing. At least one of the three husbands was made to think about the whole situation because of the incident. If these people are in any way friendly - sooner or later the one husband and the original poster will probably be able to convert the other two. Then the husbands will have problem on their hands with the lunatic wives.
But a lot of us have had those problems.
My advice is to pick away at it. I have done that with my girlfriend. I use the "don't let a good crisis go to waste" method of making progress. When the ice storm put our power out and the house was about to go to freezing - I had my reason to buy a generator. As the prices of bottled water have gone up (she drinks the bottled stuff all the time) - I have constantly said: we should get a big water processing filter. Prices of food going up: lets stock up on some more food. Guns: I claim good investment since all the stuff I have bought have gone up in price. The increase in crime reports also helps my case on keeping a gun ready in the house.
If you know these people well enough you should be able to find some way to get them thinking about this stuff. Your ultimate goal is probably to let them know that they are welcome - but make sure they understand in no uncertain terms that this is not going to be a free ride - they are going to HAVE TO bring something to the party.
If the subject gets breached even asking a simple question like: How are you going to make it all the way here from the city? What if the power is all out and the gas stations don't work (like during the ice storm), what if there are 10's of thousands of oeople on the move and the roads are all blocked? Can you walk? Ride a bike? How will you carry your stuff? With all these people out after a disaster will you be able to get your entire family to my house safely? (remind them of Katrina when the police hit the road).
One other method I have found that works to enlighten people is to constantly feed them information that backs up the point you are trying to make. I have been doing this for years with some people. Using the economic breakdown as an example - I have sent around stories and articles for quite some time to a bunch of people who were often doubters on the ideas of libertarians and those who said an economic debacle was coming. I do the same thing with my girlfriend about gun stuff and survival type things.
What I have noticed over time is that the attitudes of these people DO change. I get things parroted back to me that I know came from stuff I sent them long ago.
If you are truly worried about this and want to help these people - you will have to first (in my opinion) figure out where they stand on the topic, then you will be able to go from there to devise a plan of attack on how to help them get real about the whole situation.
Then again - you could always lie to them and say in case of SHTF you are bugging out to the upper peninsula in Michigan or some such thing - far enough you know they wont follow. That also might let them know they are on their own and get them thinking......