Tell the group that their goal is to raise the whole group off of the ground with their hands being the only things with contact to the ground (I sometimes give a time to be off the ground to sway them from trying to do simultaneous handstands). They may use each other (if you want to limit trial and error further and your group can be split into groups of 3 or 4 as those work best for the push-up) but may not use any other props. I have seen this accomplished 2 ways, the first is a group (4 works best) where each persons feet are on the lower back/thighs of another person and in the box formation they are able to do a push-up. The second way the group starts sitting in a circle (groups of 3 or 4 work best for this) and crosses their ankles, putting them on the shoulder of the person next to them and then their hands are used to lift.
Talk about communication, whose ideas were heard, what challenges were there, etc. You can also ask them initially how hard they expect it to be and at the end ask why it was harder/easier than expected.