I'm not sure what you mean by 'not enough space.' Have you ever seen a car full of clowns (or a VW Beetle in the 60's?). Space is a commodity, especially in the US. You can fit 20-30 folks in a typical house if you really need to. Or look at the Navy and the term "hot bunking."

Probably a bigger and more realistic concern would be sanitation. That could certainly suffer easily. Though I suppose that garden would suddenly flourish.

I don't know that you can motivate people. You can educate them, and encourage them to start their own preps. Or you can let them starve for a week or 2 until they realize that, "hey, being part of this commune and getting some food sounds like a good idea!" But you can't force them to figure it out. And, honestly, if you approach most people with a "world's falling apart for a year, so get ready!" approach, they're going to laugh you off or commit you for medication. Baby steps, Jeanette.

Oh, as for safety in numbers. EVERYONE should know how to shoot the guns. If only 2 people do, it's not that hard for them to get shot. Remember the scene at the end of "The 3 Amigos?"