Thanks for your comprehensive and considered responses! I have addressed some specific comments below.
Bob: very good point. Although they are all experienced summer hikers, a number of them will have little technical knowledge of things like R-ratings - I hadn't even considered this. The hot water commissary is also a good idea (although I will be encouraging them to bring as much water as possible, given it is a car camping trip).
Samuel: also some great questions/tips. A good run-up time sounds like it would be pretty handy, as then people can see if they can borrow or buy some more gear.
Tjaard: I'm not too worried about the waiver situation due to local legal conditions (MUCH less litigious than the US), the fact that it's (basically) a bunch of mates, and the fact that I have legal training. But I'll keep it in mind! A gear list sounds like a good idea. It's a group of friends from a hiking/camping club, so I know they've all got their heads well screwed on, and that they are able to summer camp. They should be fairly independent. The only issue is that they haven't camped in properly cold/snowy temperatures before.
(Edit: I know they have tents such as the Big Agnes Seedhouse UL, etc. But to me, without a good deal of knowledge to back it up, it's not appropriate for winter conditions. By 'winter' conditions, I'm talking about Australian conditions, which are not particularly severe compared to where I grew up in NZ, but can still get snow on the ground, temperatures to about -10C, and strong winds. As an aside, they all think I'm absolutely crazy for using tarp/tents in the summer hehehe.)
Bob (again): yes, I am trained in First Aid - in fact, I used to teach it to others! But good reminder - I can see who else is trained as part of my questionnaire.