For the shading we can sew a tent-like canopy with some plastic rods (see attached picture, quite generic :)) that one can push through the seams to make it stable. The rods can extend beyond the fabric so one can see when people are inside. It can be see-through one way (from inside) and transparent the other. I'll check out fabric.
We can fasten it to the roof luggage rack of the car.

I attach another sketch. The canopy shape is not a design proposal, just an idea how to place the canopy. Its shape doesn't accommodate enough people, so that has to change.