They're very different aeroplanes.
The C42 is much better handling, much cheaper to run, shorter field but needs greater owner engagement with maintenance. It also has a significantly lower wing loading making behaviour in turbulence poorer, payload is essentially two pilots and a toothbrush, and it'll be day-VFR only. The engine will be much more frugal, but is a totally different entity to use and look after.
In essence, it's a switch to a completely different form of flying. A thoroughly enjoyable one, but if you are all used to planning your flying around what a C172 can do, you are somewhat doomed to surprise and disappointment. If your plan is to simply cost save and carry on with the sort of flying you've done before, this is the wrong plan.
I'd suggest go to a microlight school and all get a few hours in one before taking the leap. It might work wonderfully for you all, but it might not.
G